[Documentation] Encode rules for skeleton, asserts, unrecheable, testing, etc

[bcardosolopes]

Inspired by @Lancern work on providing some ASM guideline goodness, I created some guidelines for auto and camelCase usage, see it here: https://llvm.github.io/clangir/GettingStarted/coding-guideline.html

However, we still need to encode the other common review items, such as OG skeleton, asserts, unrecheable, testing, etc. It'd be nice to have that.