version-control: Add README.md and instructor.md from the guide

version-control: Add README.md and instructor.md from the guide

Move instructor hints (For Instructors section) and subject outlines
("understand" and "keypoints" classes) from the instructor guide [1]
into the boot camp repository.  This is currently targeted at
Subversion, but making these notes tool-agnostic will come in the next
commit.  Here I just copy the guide content over while translating it
to Markdown.

For posterity, I've grafted on the guide history.  Here's how I
extracted the svn.html history from the guide repository:

1. Start a new branch in the earlier guide repository:

  $ git checkout -b wip d013cab

2. Limit history to svn.html:

  $ git filter-branch -f --prune-empty \
  > --index-filter 'git rm --cached --ignore-unmatch $(git ls-files | grep -v svn.html)' \
  > HEAD

3. Drop no-op merges:

  $ git rebase -i 0025ac4

Then I cherry-picked my original boot-camps commit (c1330e0) onto the
result to create this commit:

  $ git cherry-pick c1330e0
  $ git rm svn.html
  $ git commit --amend

[1]: https://github.com/swcarpentry/guide