Update CONTRIBUTING.md

CONTRIBUTING.md

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-# LLVM-based Bolt Compiler
+# Contributing to Bolt
 
-This directory contains a partial implementation of the Bolt programming
-language using C++ and LLVM. It currently is one of the main contenders of
-becoming the offical Bolt compiler.
+So you want to contribute something to the Bolt language or its compiler? That's
+great! We're so glad to have you!
 
-## Developing
+## Preliminary Knowledge
 
-You need a recent version of the Zen libries to be able to compile. If youu
-still get build errors, the Zen libraries might be out of date. Do not hesitate
-to file an issue!
+### Type Checking
+
+Here are some resouces to get started with type checking, ordered from high-level overview to deep dive:
+
+- [Hindley-Milner Type System](https://en.wikipedia.org/wiki/Hindley%E2%80%93Milner_type_system)
+- [Write You A Haskell](https://smunix.github.io/dev.stephendiehl.com/fun/index.html), most notably [this implemenation](https://github.com/sdiehl/write-you-a-haskell/tree/master/chapter7/poly_constraints)
+- [Type Inference blog posts by Thunderseethe](https://thunderseethe.dev/posts/type-inference/)
+- [Typing Haskell in Haskell](https://gist.github.com/chrisdone/0075a16b32bfd4f62b7b)
+- [The Essence of ML Type Inference](http://gallium.inria.fr/~fpottier/publis/emlti-final.pdf)
+
+## Building
+
+### 1. Check out the sources
+
+```sh
+git clone https://github.com/boltlang/bolt
+git clone https://github.com/samvv/zen bolt/deps/zen
+```
+
+You need the most recent version of the Zen libries to be able to compile. If
+you still get build errors, the Zen libraries in the repositories might be out
+of date. Do not hesitate to file an issue!
 
 This is how a potential invocation to CMake could look like: