Add ungrammar extensions

Author: azdavis

src/tools/rust-analyzer/lib/ungrammar/README.md

@@ -1,6 +1,21 @@
 # ungrammar
 
-A DSL for specifying concrete syntax trees. See this
-[introductory post](https://rust-analyzer.github.io/blog/2020/10/24/introducing-ungrammar.html).
+A DSL for specifying concrete syntax trees.
+
+See the [blog post][post] for an introduction.
 
 See [./rust.ungram](./rust.ungram) for an example.
+
+## Editor support
+
+- Vim
+  - [vim-ungrammar][]
+  - [ungrammar.vim][]
+- VSCode
+  - [ungrammar-tools][]
+
+[post]:
+  https://rust-analyzer.github.io/blog/2020/10/24/introducing-ungrammar.html
+[vim-ungrammar]: https://github.com/Iron-E/vim-ungrammar
+[ungrammar.vim]: https://github.com/drtychai/ungrammar.vim
+[ungrammar-tools]: https://github.com/azdavis/ungrammar-tools