Now you can access gitweb at http://yourserver/gitweb by simply adding
this to configuration.nix (assuming services.lighttpd.enable = true);
services.lighttpd.gitweb.enable = true;
The path to all bare repositories served by gitweb can be set with this
option (default value below):
services.lighttpd.gitweb.projectroot = "/srv/git";
Based on patch contributed by Bjørn Forsman.