feat(wpcarro/marcus): Support home-manager

For now:
- git confg
- picom: X compositor
- dunst: system notifications (not working for quassel)

I still need to port various configs and ensure I support both gLinux and NixOS
machines.

Change-Id: I31a635eaacac25ef6219e079fc968d2ece026a5f
Reviewed-on: https://cl.tvl.fyi/c/depot/+/4736
Reviewed-by: wpcarro <wpcarro@gmail.com>
Autosubmit: wpcarro <wpcarro@gmail.com>
Tested-by: BuildkiteCI

users/wpcarro/dotfiles/default.nix

@@ -0,0 +1,5 @@
+{ ... }:
+
+{
+  dunstrc = ./dunstrc;
+}