Added CONTRIBUTING.md : WIP

[gaurava05]

Fixes #799

Added the CONTRIBUTING.md file in the repo and linked it inside the newly created "Contributing" section of the README.md

Changes

• Added a "Contributing" section in the README.md file with the link to the newly created CONTRIBUTING.md file and a link to join our Slack workspace
• Created a new CONTRIBUTING.md file with the text by @Jaifroid mentioned in Issue Update documentation to include new implementation #792
• Added instruction to carry out extension version testing in the browser(needs review here @Jaifroid )

Flags

Needs review in the following changes:

• Testing the extension versions locally (line number 21-23 in CONTRIBUTING.md)
• Here, I mentioned just for the chrome, how can we cover other platforms too? Also, should we also link instructions to load an extension's source code in the browser
• Added Slack link in the README.md's contribution section for the ease of newcomers, is it fine?

Related Issues

• Issue Update documentation to include new implementation #792

[Jaifroid]

Thank you for this useful PR. Just some minor changes as suggested in the review comments, please.

[gaurava05]

@Jaifroid thanks for your useful review. Will make the necessary changes.

[gaurava05]

@Jaifroid pushed another commit with the required changes. Please review at your convenience.

[Jaifroid]

Thank you, it's looking good now! I'll request a review from Mossroy.

[mossroy]

There's a file with the same name in https://github.com/kiwix/overview/blob/master/CONTRIBUTING.md , that covers the basic steps for creating a PR.

I prefer your file, but it might be worth pointing to an external documentation that explains how to create a PR on github

[Jaifroid]

Thanks for the latest. All fine for me now!

[Jaifroid]

@gaurav7019 Thanks for this PR! We can merge it now. Are you ready for me to squash/merge (it will still appear as your PR)?

[gaurava05]

@gaurav7019 Thanks for this PR! We can merge it now. Are you ready for me to squash/merge (it will still appear as your PR)?

Yeah sure, go ahead. It was a great first experience. 😄