Add contributing rules

[Pabl0cks]

Added a Rules section to the CONTRIBUTING.md to:

• Make the need of creating Issues before PRs a bit clearer
• Be able to prevent "sybil contributions" by fixing small spelling or grammatical errors, just for the sake of farming airdrops.

Got inspired by: https://github.com/wevm/viem/blob/main/.github/CONTRIBUTING.md

[carletex]

Good stuff @Pabl0cks thanks!!

I added some little fixes in the file while we are at it

[technophile-04]

This is great thanks Pablo!