Update README.md

Author: swyxio

README.md

@@ -95,6 +95,7 @@ There also exist helper type libraries:
 - [type-fest](https://github.com/sindresorhus/type-fest)
 - [tsdef](https://github.com/joonhocho/tsdef)
 - [rex-tils](https://github.com/Hotell/rex-tils)
+- [ts-toolbelt](https://github.com/pirix-gh/ts-toolbelt) ([Reddit](https://www.reddit.com/r/typescript/comments/c2nq7k/higher_type_safety_for_typescript_with_tstoolbelt/))
 
 seriously, check some of these out, they represent a ton of accumulated typescript experience.