docs: update todo, reminder in Config to update readme

crates/pacdef_core/src/config.rs

@@ -5,6 +5,7 @@ use std::path::Path;
 use anyhow::{bail, Context, Result};
 use serde_derive::{Deserialize, Serialize};
 
+// Update the master README if fields change.
 /// Config for the program, as listed in `$XDG_CONFIG_HOME/pacdef/pacdef.yaml`.
 #[derive(Debug, Serialize, Deserialize)]
 pub struct Config {