Document SourceTree flow

Description

SourceTree works with GitLab, but the integration is unintuitive and undocumented. We should document how use SourceTree with GitLab.

Proposal

Links / references

• http://jaredleonmorgan.net/2016/03/16/Using-Source-Tree-to-Access-Git-Lab.html
• https://stackoverflow.com/questions/27570370/how-to-integrate-sourcetree-for-gitlab

Documentation blurb

Overview

What is it? Why should someone use this feature? What is the underlying (business) problem? How do you use this feature?

Use cases

Who is this for? Provide one or more use cases.

Feature checklist

Make sure these are completed before closing the issue, with a link to the relevant commit.

• Feature assurance
• Documentation
• Added to features.yml