add CONTRIBUTING.md

* move contributing instructions here
* add lightweight contributor agreement

If a contributing doc exists in the repo,
Github links to it from a new Pull Request
and new issue form.

Signed-off-by: Paul Morgan <jumanjiman@gmail.com>
gemspec: update base data

after this commit, we can actually build a gem

Signed-off-by: Paul Morgan <jumanjiman@gmail.com>
Rakefile: use bundler to bootstrap clean environment

* use a clean environment when doing dev on this gem
* provide helpful instructions to somebody who is not a ruby expert

Signed-off-by: Paul Morgan <jumanjiman@gmail.com>
gemspec: add dev dependencies for running tests

Runtime deps should not be as strict as dev deps since
this gem will be used as a dev dependency for other repos.