update README

README.md

@@ -1,24 +1,71 @@
 # pacdef
+
 multi-backend declarative package manager for Linux
 
 
 ## Installation
+
 `pacdef` is available in the AUR [as stable release](https://aur.archlinux.org/packages/pacdef) or [development version](https://aur.archlinux.org/packages/pacdef-git), and on [crates.io](https://crates.io/crates/pacdef).
 
+The AUR package will also provide completions for `zsh`.
+If you use the `crates.io` version you will need to copy the completion file to the right directory yourself.
+
 
 ## Use-case
-`pacdef` allows the user to have consistent packages among multiple Linux machines by managing packages in group files.
-The group files are maintained outside of `pacdef` by any VCS, like git. 
 
-<!-- TODO There's something missing here. -->
+`pacdef` allows the user to have consistent packages among multiple Linux machines by managing packages in group files.
+The idea is that (1) any package in the group files ("managed packages") will be installed explicitly, and (2) explicitly installed packages *not* found in any of the group files ("unmanaged packages") will be removed.
+The group files are maintained outside of `pacdef` by any VCS, like git. 
 
 If you work with multiple Linux machines and have asked yourself "*Why do I have the program that I use every day on my other machine not installed here?*", then `pacdef` is the tool for you.
 
 
-## Supported backends
+## Of groups, sections, and packages
-At the moment, supported backends are limited to the following.
 
-<!-- TODO explain what sections are -->
+`pacdef` manages multiple package groups (group files) that, e.g., may be tied to a specific use-case.
+Each group has one or more section(s) which correspond to a specific backend, like your system's package manager (`pacman`, `apt`, ...), or your programming languages package manger (`cargo`, `pip`, ...).
+Each section contains one or more packages that can be installed respective package manager.
+
+
+### Example
+
+Let's assume you have the following group files.
+
+`base`:
+
+```ini
+[arch]
+paru
+zsh
+
+[rust]
+pacdef
+topgrade
+```
+
+`development`:
+
+```ini
+[arch]
+rustup
+rust-analyzer
+
+[rust]
+cargo-tree
+flamegraph
+```
+
+Pacdef will make sure you have the following packages installed for each package manager:
+
+- Arch (`pacman`, AUR helpers): paru, zsh, rustup, rust-analyzero
+- Rust (`cargo`): pacdef, topgrade, cargo-tree, flamegraph
+
+Note that the name of the section corresponds to the ecosystem it relates to, rather than the package manager it uses.
+
+
+## Supported backends
+
+At the moment, supported backends are limited to the following.
 
 | Package Manager | Section   | Application |  Notes                                               |
 |-----------------|-----------|-------------|------------------------------------------------------|
@@ -29,6 +76,7 @@ Pull requests for additional backends are welcome!
 
 
 ### Example
+
 This tree shows my pacdef repository (not the `pacdef` config dir).
 ```
 .
@@ -49,71 +97,21 @@ This tree shows my pacdef repository (not the `pacdef` config dir).
 └── pacdef.conf
 ```
 
-* The `base` group holds all packages I need unconditionally, and includes things like zfs,
+- The `base` group holds all packages I need unconditionally, and includes things like zfs,
   [paru](https://github.com/Morganamilo/paru) and [neovim](https://github.com/neovim/neovim).
-* In `xorg` and `wayland` I have stored the respective graphic servers and DEs.
+- In `xorg` and `wayland` I have stored the respective graphic servers and DEs.
-* `wireless` contains tools like `iwd` and `bluez-utils` for machines with wireless interfaces.
+- `wireless` contains tools like `iwd` and `bluez-utils` for machines with wireless interfaces.
-* Under `hosts` I have one file for each machine I use. The filenames match the corresponding hostname. The packages
+- Under `hosts` I have one file for each machine I use. The filenames match the corresponding hostname. The packages
   are specific to one machine only, like device drivers, or any programs I use exclusively on that machine.
 
 Usage on different machines: 
-* home server: `base private hostname_a`
-* private PC: `audio base desktop private rust wayland hostname_b`
-* work PC: `base desktop rust work xorg hostname_c`
 
+- home server: `base private hostname_a`
+- private PC: `audio base desktop private rust wayland hostname_b`
+- work PC: `base desktop rust work xorg hostname_c`
 
-## How to use
-* import one or more groups: `pacdef import base desktop audio`
-* install packages from the imported groups: `pacdef sync`
-* show packages that are not part of any group: `pacdef unmanaged`
-* remove packages that are not in any group: `pacdef clean`
-* show imported groups: `pacdef groups`
-* create a new group: `pacdef new temp` (use `new -e` to edit the file right away)
-* remove a previously imported group: `pacdef remove audio`
-* review all unmanaged packages interactively: `pacdef review`
-* search for the group that contains a package: `pacdef search firefox`
-* show packages of a group: `pacdef show desktop`
-
-`pacdef import`ing a package group file creates a symlink to that file in `pacdef`'s config dir, thereby letting `pacdef` know you want to have the packages in this file on your machine.
-Then installing all packages from all groups is as simple as `pacdef sync`.
-All package operations are executed by the respective package managers.
-
-
-### Configuration
-
-On first execution, it will create a basic config file under `$XDG_CONFIG_HOME/pacdef/pacdef.yaml`.
-
-```yaml
-aur_helper: paru  # AUR helper to use on Arch Linux (paru, yay, ...)
-aur_rm_args: null  # additional args to pass to AUR helper when removing packages (optional)
-warn_not_symlinks: true  # warn if a group file is not a symlink
-```
-
-### Package group files
-<!--- TODO explain sections --->
-Group files loosely follow the syntax for `ini`-files.
-
-1. One package per line. 
-2. Anything after a `#` is ignored.
-3. Empty lines are ignored.
-4. If a package exists in multiple repositories, the repo can be specified as prefix followed by a forward slash.
-   The AUR helper must understand this notation.
-
-Example:
-```ini
-[pacman]
-alacritty
-firefox  # this comment is ignored
-libreoffice-fresh
-mycustomrepo/zsh-theme-powerlevel10k
-
-[rust]
-cargo-update
-topgrade
-```
 
 ## Naming
 
 `pacdef` combines the words "package" and "define".
 
-