git -> Git where appropriate

git -> Git where appropriate

W. Trevor King: The conflicts with the original f3bc1dd [1] were
trivial, involving the YAML front matter introduced by 208c61f (Add
header material and author to git and GitHub lesson, 2013-11-06).  I
haven't included 208c61f in this history because:

* This Markdown source is not necessarily destined for Jekyll.
* The author information is clear from the Git history, and explicit
  author listings in text itself are hard to keep up to date.

[1]: https://github.com/swcarpentry/bc/pull/133

Conflicts:
	instructor.md