Make documentation guidelines easier to discover
Created by: ryan-blunden
- Added a link to the documentation guidelines from the engineering home page page index to help with discovery.
- Moves the documentation page into the engineering directory
- Added a paragraph to the documentation page explaining its documentation for the sourcegraph repo while also adding link for editing the handbook
- Added a link to editing the handbook on the handbook home page
- Added a > NOTE section to the handbook usage page to clarify that the documentation page is for adding info about using or configuring Sourcegraph (the product).