Per @hmistry's suggestions, I've moved the development instructions outside of the bulleted list and made it its own sentence. And I've shortened the copy under the "Contributing to Bundler" header.

Hey team,

As part of an ongoing effort to revamp the docs, I've been working with @indirect to rewrite the contributor guidelines README. We wanted to streamline the way the information was laid out, and make it more explicit to potential contributors how they can contribute and what next steps they needed to take. We condensed everything down to three sections (a general guidelines section, contributor section, and a new, supporting Bundler section). Everything links out to existing documentation.

Github has defined a couple of tags to use for classifying issues that are suitable for new contributors to fix/contribute towards. We have started using these tags in Github so we should start linking to them in our documentation as well.

used relative path instead of full url