Improve contributing docs

[evamaxfield]

While helping onboard a new contributor a few issues encountered were:

• "Deploying" is confusing when we are an infrastructure project. Thought this meant "deploying to google cloud" when it means "Releasing a new version of the backend"
• Also thought that she was meant to deploy an infrastructure to contribute. Need to make this much more clear that it is entirely possible (and encouraged) to contribute to CDP without needing to deploy a dev infrastructure

[isaacna]

Hm yeah I guess we do throw around "deploy" and "deployment" a lot which could be confusing. I'll see if I can make the wording more clear.

I'm not sure if this is mentioned in the docs clearly, but maybe we could further emphasize the cdp-backend is just a library and that deployments come from separate repos spawned using cookicutter as a template

[evamaxfield]

Strong agree. These docs should very explicitly mention that to contribute to the backend you do not need a dev deployment. In some cases it helps but a larger majority of issues and features can be done without dev infra.