Documentation: Add Troubleshooting for Windows users without Password

This Guide https://gitlab.com/gitlab-org/gitlab-ci-multi-runner/blob/master/docs/install/windows.md Tells you to enter your Windows Password. If you don't have a Windows Password multi-runner service won't start.

To fix this, read Microsofts page (see: How to Configure the Service to Start Up with the Built-in System Account): https://support.microsoft.com/en-us/kb/259733

Maybe we should add a Link to this Microsoft Page, either in docs/install/windows.md or in docs/faq/README.md