Add how to contribute md to github project

I will work on this and do code review with and .

I am cleaning up stale branches in the repo. In branch, here is what we have for CONTRIBUTING.md:

I am looking at the Pypa Package Guide on Contributing to their project and wonder how much if we can copy their format: https://packaging.python.org/contribute/

Though this is also evoke a question of how and what we want our contributors to contribute. For example, the Synapse Python client is a part of the Synapse platform. Features and bug fixed in the Synapse Python client are prioritize and put into Epic. The fundamental question we ask for each Jira ticket is whether we should be working on the ticket, not just the concern about the engineering effort, but also, about whether the feature should be in the clients.

I would like to weight in on what is the scope of external contributions (outside of the Synapse engineering team). We do have documentation on how an engineer can contribute. But before extending it to external contributor, we should evaluate what and how we want to receive contributions, as it also requires PM efforts in reviewing the topic and engineering effort in reviewing the code.

I will mark this as Blocked until and I discuss a strategy moving forward.

In discussion with , , and others, we'd like to move forward with the proposed text in the above comment. The triage of issues by the engineering team, PM, or Sage as an organization can be a separate conversation.

I opened a PR for this to use the text as above for review.

https://github.com/Sage-Bionetworks/synapsePythonClient/pull/698