Update README.md

Closes #32.

Author: josevalim

README.md

@@ -4,6 +4,8 @@
 
 Elixir grammar for [tree-sitter](https://github.com/tree-sitter/tree-sitter).
 
+Ready for production. Currently used by GitHub itself for source code highlighting and code navigation.
+
 ## Development
 
 See [the docs](./docs/index.md) for more details.