Expand on Growth company value and add initiatives and resources

Created by: marekweb

"Continuously grow" is one of our company values but it currently has less detail and explanation than the other values . Yet this is an important value and it intersects with a lot of the things we do at Sourcegraph.

This PR is an attempt to improve this by expanding on the description of the "Continuously grow" value, adding more details about how we live this value, and listing initiatives and resources that tie into it.

Hopefully as we grow more internal initiatives in growth, learning & development, and education we can add more to this section.