Create CONTRIBUTING.md

[daribock]

I think we should create a CONTRIBUTING.md so other people know how to contribute to our project.
Also we should standardize our commits.
I know two commit methods.

1. With a reference at the front.

• Commit that doesn't refers to an issue:
  [NoRef-0] (commit message)
• Commit that refers to an issue:
  [Ref-#(issue or pull request number)] (commit message)

2. Gitmoji/gitmoji-cli

• Gitmoji is an initiative to standardize and explain the use of emojis on GitHub commit messages
• And gitmoji-cli provides an easy solution for using gitmoji from the command line

What do you think? Which one is better or do you know an even better method to standardize our commits?