docs(contributing): Create contributing guide

[k911]

Should include following topics:

• [x] Making first contribution :heavy_check_mark:
• [x] Rebasing branch with develop :heavy_check_mark:
• [x] Commitizen usage :heavy_check_mark:
• [x] Conventions :heavy_check_mark:
• [x] PR Policy (Squash or Rebase) :heavy_check_mark:

If you'd like to help @knit-pk/web please add commits directly to this branch we'll squash them

[FieryCod]

@k911 Seems legit for me. May I merge this? Good job!!!

[k911]

I'd like to add this ones in this PR too:

• Rebasing branch with develop
• Commitizen usage
• Conventions (generally add links to docs/)
• PR Policy (Squash or Rebase)

[FieryCod]

Ok, so we will patiently wait for it! 👍

[k911]

I think it is ready now.

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[FieryCod]

Good job @k911! 👍 🎉 🎉