git: configure a better log format

hosts/common/programs/git.nix

@@ -5,14 +5,22 @@ let
 in
 {
   sane.programs.git.fs.".config/git/config".symlink.text = mkCfg {
+    # top-level options documented:
+    # - <https://git-scm.com/docs/git-config#_variables>
+
     user.name = "Colin";
     user.email = "colin@uninsane.org";
+
     alias.co = "checkout";
+
     # difftastic docs:
     # - <https://difftastic.wilfred.me.uk/git.html>
     diff.tool = "difftastic";
     difftool.prompt = false;
     "difftool \"difftastic\"".cmd = ''${pkgs.difftastic}/bin/difft "$LOCAL" "$REMOTE"'';
     # now run `git difftool` to use difftastic git
+
+    # render dates as YYYY-MM-DD HH:MM:SS +TZ
+    log.date = "iso";
   };
 }