doc(man): add pip_binary config value

man/pacdef.toml.5

@@ -48,6 +48,10 @@ Warn if any group file is not a symlink and is not a child of a symlinked dir in
 .B flatpak_systemwide = true
 Whether flatpak packages should be installed system-wide or per user.
 
+.TP
+.B pip_binary = pip
+Whether pipx instead of pip should be used for Python package management.
+
 .SH SEE ALSO
 .BR pacdef(8)