Add gh workflows badges (#1251)

Co-authored-by: Junyoung/Clare Jang <[email protected]>

Author: jneira

README.md

@@ -2,6 +2,8 @@
 
 [![License Apache 2.0][badge-license]][license]
 [![CircleCI][badge-circleci]][circleci]
+![Github Testing Workflow](https://github.com/haskell/haskell-language-server/workflows/Testing/badge.svg)
+![Github Nix Workflow](https://github.com/haskell/haskell-language-server/workflows/Nix/badge.svg)
 
 [badge-license]: https://img.shields.io/badge/license-Apache2-green.svg?dummy
 [license]: https://github.com/haskell/haskell-language-server/blob/master/LICENSE