[GSoD 2021] Improved contributing guidelines

[iamrajiv]

Fixes: #1111
Related: #1012 wechaty/grpc#140 wechaty/openapi#16

[Rohitesh-Kumar-Jain]

You haven't attached all the ss

[Rohitesh-Kumar-Jain]

We probably should also add some guidelines about adding relevant labels regarding the PRs and Issues.

[Rohitesh-Kumar-Jain]

We probably can also add the Code of Conduct and Getting Help sections in which include a link to the Wechaty Gitter channel as well.

[proudofsimin]

We could talk about the style more, but as in my previous experience and Google standards, we are actually trying to eliminate using "you" in documents to make the tone soften and formal. I understand that each document has its own writing style and those Django used don't necessarily apply to Wechaty's.

[Rohitesh-Kumar-Jain]

Thanks for implementing my suggestion : )