collaborating chapter (4) - engaging section

[billspat]

Write the section in the "collaboration" chapter describing how to use pull requests to add to features of an existing project, either external or internal to your group.

please review the following as source material for this section , which may cover the bulk of what we want to cover, and the aspect of the course is to simplify and walk people through the concepts here.

https://git-scm.com/book/en/v2/GitHub-Contributing-to-a-Project

[billspat]

@kellykapsar this is the last section of this chapter and I'll take it on. I initially assigned both of us but this issue is just for the section on pull requests, and I am self-assigning it