Add a page on GoLand setup to Sourcegraph docs

Created by: vrto

Description

Add a page on GoLand to Sourcegraph docs. This is more of a skeleton page, and I hope developers will pick it up and extend as we continue developing Sorucegraph and learning useful GoLand tips and tricks.

Test plan

Manual QA-ing, like this:

• run sg start
• navigate to http://localhost:5080/dev
• click on the GoLand link in the Tools section that links to http://localhost:5080/dev/background-information/goland
• inspect the page