Developer workflow

Adds two documentation files: `developer-workflow.md` and `admin-workflow.md`.  These files, especially `admin-workflow.md`, are probably not ready for merging.  I have created the pull request to make it easy for developers to comment on the files
 - developer-workflow.md documents workflow for developers.  This could be merged with one possible exception.  I did *not* include @mo-nathan's recommendation to setup Github .ssh access based on https://help.github.com/articles/generating-ssh-keys.  I am not opposed to this; rather I see that Github recommends https access (at least for cloning).  See https://help.github.com/articles/which-remote-url-should-i-use.  I don't understand the plusses and minuses of each, or why Github recommends https. (Maybe because of two-factor authentication?)