Add page to docs on open company and open product

Created by: ryan-blunden

This info was previously available as a blog post on sourcegraph/about but there needs to be a point of reference about Sourcegraph's philosophy of developing in the open.

Catalyst for this was wanting to link to such a page from the latest 3.2 blog post as it discusses how we develop in the open and the benefits that has for getting input on the product roadmap.