Pull in Git history from runC repository

[wking]

CONTRIBUTING.md and MAINTAINERS_GUIDE.md from #1 came out of
opencontainers/runc but lost their history. Since dropping history
like that makes Signed-off-by tags less useful, this PR restores the
history extracted from the runC repository. The branch was
constructed with:

$ git remote add --no-tags runc git://github.com/opencontainers/runc.git
$ git fetch runc
$ git checkout runc/master
$ git filter-branch -f --prune-empty --index-filter 'git rm --cached $(git ls-files | grep -v "^\(libcontainer/\|hack/\)\?\(CONTRIBUTING.md\|LICENSE\|MAINTAINERS_GUIDE.md\|CONTRIBUTORS.md\|CONTRIBUTORS_GUIDE.md\|MAINTAINERS.md\)$")'
$ COMMITS=$(git log --no-merges --oneline | grep -v 'Initial commit' | cut -f 1 -d ' ' | tac)
$ git checkout --orphan runc-history
$ git rm -rf .
$ for COMMIT in $COMMITS; do git cherry-pick $COMMIT; done
$ git rebase -i 'HEAD^{/Move libcontainer documenation to root of repo}^'
$ git checkout 'HEAD^{/Move libcontainer into subdirectory}^' -- LICENSE
$ git commit --amend --no-edit
$ git rebase --continue
$ diff <(git ls-tree runc/master) <(git ls-tree HEAD)
# no differences in the files we're pulling out
$ git merge origin/master
# resolve conflicts
$ git show --format=%T origin/master
72e1e27f32b0d90129fdbf31f1de471d90437347
$ git show --format=%T HEAD
72e1e27f32b0d90129fdbf31f1de471d90437347

Pulling in the LICENSE as well makes the Signed-off-by assertions
useful, even though that's (almost) the same content that already landed in
this repo via ad517c3.

[caniszczyk]

@crosbymichael any opinion here? I don't think we need the full history

[crosbymichael]

Ya, not really a need here as we are already modifying it. Its nice to have a fresh and clean history for these docs.