introduce epicast development guide

[dfarrow0]

• includes detailed instructions for local development, checking code
  into the dev branch, and cherry-picking code over to the prod branch
• the guide lives in the master branch since it is about the
  development process in general, and is not specific to the the dev
  branch

[dfarrow0]

@krivard @korlaxxalrok @ChrisSheng97 FYI

[krivard]

What's the reasoning behind using cherry-pick instead of merge, is it for deploy.json purposes? If so, we may want to add a section about how to rebase a set of changes into a single commit, to reduce the number of cherry-picks (and thus the number of times something can go wrong) necessary to import a change.

[dfarrow0]

Not necessarily for deploy.json. I envision a scenario where multiple features/fixes are in-flight on the dev server at any given time. On Friday, some of those features will be ready for prime-time, while others aren't quite ready yet. I recommend cherry-pick to grab the specific commits which are ready to go to prod while leaving other commits behind in the dev chain.

Feel free to add that section though, especially if what you suggested is your expected workflow.