direnv: add add_extra_vimrc hook [skip ci]

* also provide .vimrc-example, it  would be picked up when renamed to
  plain .vimrc
* also add .vimrc to .gitignore as there this .vimrc is supposed to have
  personal editor configurations (it doesn't have to but I am not going
  to impose editor configs on anyone, hence if anyone uses it, it's
  personal)

.envrc

@@ -1 +1,5 @@
 use flake
+
+# ref: https://github.com/direnv/direnv/wiki/Vim
+# comment out if not planning to use this
+add_extra_vimrc

.gitignore

@@ -1,3 +1,4 @@
 .direnv
 result
 result-*
+.vimrc

.vimrc-example

@@ -0,0 +1,4 @@
+augroup vimgo_local
+	au!
+	au FileType go nmap <leader>gr :term ++hidden ++open nixGL go run -v .<cr>
+augroup END