Add docs to deploy on GCP Cloud Shell

[rahulkumaran]

I'm submitting a ... (check one with "x")

• [ ] bug report
• [ ] feature request
• [ ] support request => Please do not submit support requests here, instead ask your query in out Gitter channel at https://gitter.im/fossasia/meilix

Actual Behaviour No docs that support how to deploy the app on GCP

Expected Behaviour Currently we have steps to deploy on Heroku. I think it would be great to have a doc to show people how to deploy this on GCP's Cloud Shell too. Gives people more flexibility to deploy.

Other information:

I'll take people through how to deploy it in a step by step manner.

Would you like to work on the issue? Yes, would love to.

[meets2tarun]

Yes, this can also be implemented.

[sarnava1]

Yes this could be one nice feature. I saw your youtube video where you were teaching about gcp deployment.