both: add developer contribution guidelines

[yss14]

Since we want to search for new voluntary contributors for this project, we require some basic developer contribution guidelines. Those should include:

• general git workflow
• frontend specific guidelines
• backend specific guidelines

[udayrajMT]

Hi 👋 Just giving a heads up - I'd like to tune in on this in near future(currently finishing up a project that uses react & type-graphql). Interested to explore this project(more on the frontend side) and contribute if I can :)

[yss14]

@udayrajMT Sounds great! I'm currently migrating the frontend data layer from apollo client to react-query. Hopefully, after that I will have time for some docs on contribution :) What would you prefer as a communication channel?