Document how to use Visual Studio with GitLab

Description

From https://gitlab.slack.com/archives/C0NFPSFA8/p1501024891591663:

most IDEs (like Visual Studio) have a vanilla Git plugin that will works with GitLab

We should document how to use Visual Studio with GitLab

Proposal

Links / references

• https://marketplace.visualstudio.com/items?itemName=MysticBoy.GitLabExtensionforVisualStudio

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