clean up and improve docs

modules/common/shell/charm.nix

@@ -1,5 +1,7 @@
 { config, pkgs, lib, ... }: {
 
+  # Convenience utilities from charm.sh
+
   options.charm.enable = lib.mkEnableOption "Charm utilities.";
 
   config.home-manager.users.${config.user} = lib.mkIf config.charm.enable {

modules/common/shell/direnv.nix

@@ -1,5 +1,6 @@
 { config, ... }: {
 
+  # Enables quickly entering Nix shells when changing directories
   home-manager.users.${config.user}.programs.direnv = {
     enable = true;
     nix-direnv.enable = true;

modules/common/shell/fzf.nix

@@ -1,5 +1,7 @@
 { config, ... }: {
 
+  # FZF is a fuzzy-finder for the terminal
+
   home-manager.users.${config.user} = {
 
     programs.fzf.enable = true;