Create git-basics.md

I added a document git-basics.md to the meta folder.  My goal was to find a balance between being specific enough to be useful but general enough to apply to other projects.  I could see other projects copying this verbatim, and as long as they have another document git-workflow.md in the same folder that fills out the details, it should be fine.  Of course, I think we can improve upon our own git-workflow, in particular giving the specific fetch/rebase/push and pull request steps.