README: add `insta` crate into projects using pest
See:
@@ -150,6 +150,7 @@ Digit: 2
* [handlebars-rust](https://github.com/sunng87/handlebars-rust)
* [hexdino](https://github.com/Luz/hexdino)
* [Huia](https://gitlab.com/jimsy/huia/)
+* [insta](https://github.com/mitsuhiko/insta)
* [jql](https://github.com/yamafaktory/jql)
* [json5-rs](https://github.com/callum-oakley/json5-rs)
* [mt940](https://github.com/svenstaro/mt940-rs)
