[WIP] Boot camps history restore

**Please do not merge this Pull Request yet**

This injects about 6 MB of `boot-camps` history into the `bc` repository, specifically all history for files in the tree at https://github.com/swcarpentry/boot-camps/commit/5b42aeb0492c8d581c77619514fbfbffc2045c19.

I got here by following these steps:

## Cleaning up boot-camps

```
git ls-files > keep-these.txt
git filter-branch --force --index-filter "git rm  --ignore-unmatch --cached -qr . ; cat $PWD/keep-these.txt | gxargs git reset -q \$GIT_COMMIT --" --prune-empty --tag-name-filter cat -- --all
rm -rf .git/refs/original/
git reflog expire --expire=now --all
git gc --prune=now
git gc --aggressive --prune=now
```

## Merging in history with state reset to current state of bc
```
git branch bc-first-commit 328d742231cea360e11469b8a024e20d0686e723
git read-tree --reset bc-first-commit
git commit -m "Sync with bc original state"
git merge bc-first-commit
git clean -xdf
git checkout README.md
git merge --no-ff swcarpentry/gh-pages
```

This PR needs discussion and review before we merge it in.  

We should check that 

*It actually restores commit history/provenance of files
*I've actually gotten the right balance of size vs. preserved history
*I haven't missed anything important