Docs explain how Windows and Powershell works fine for git

What does this MR do?

A colleague was confused when searching high and low for the .ssh directory, only to understand from me that if it's not there he just never used SSH before. So I explain that here.

Then I realized that the docs don't show that Powershell and Git for Windows with OpenSSH for Windows works just fine for using git. So I explained that as well.

I also removed the sentence stating that GitLab doesn't install on Windows, as that seemed irrelevant there and confusing at best.

Does this MR meet the acceptance criteria?

Conformity

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