add coc extension readme (#343)

Author: amiralies

editor-extensions/coc.nvim/README.md

@@ -0,0 +1,26 @@
+# coc-reason
+
+Reason language server extension for [`coc.nvim`](https://github.com/neoclide/coc.nvim).
+
+## Install
+
+1. Inside (neo)vim run this command:
+
+```
+:CocInstall coc-reason
+```
+
+Note: for coc installation instructions visit [`coc.nvim`](https://github.com/neoclide/coc.nvim/wiki/Install-coc.nvim) repo
+
+## Features
+* Code completion
+* Go to definition
+* Diagnostics
+* Find references
+* Hover for type info
+* Format file
+
+## License
+
+MIT
+