git: add local git config

.config/git/config

@@ -53,3 +53,6 @@
 	reset-head = remote set-head origin -a
 	head = for-each-ref --format="%(symref:lstrip=-1)" refs/remotes/origin/HEAD
 	sh = "!git switch $(git head)"
+
+[include]
+	path = ./config.local

.gitignore

@@ -5,6 +5,7 @@
 !.config
 !.config/git
 !.config/git/**
+.config/git/config.local
 !.config/nixpkgs
 !.config/nixpkgs/**
 !.local