Further development on command line tutorial (#1699)

* Directory to folder for consistency

* Added explanations, links, headings

* Rewording, additions, and so on

* Renamed file, underlined os-agnostic section

* Update link

* A suggestion about the hotkeys section; small other changes

* A screenshot about git for Windows mouse settings

* Added some tips, reworded some content

* Reworded relation to linked tutorial

Simplified command in script

* Add explicit path to commands

* Remove/add empty lines for consistency

* More compact screenshot

* Fixes, rewordings, clarifications

* Added a few words on commands

* Minor corrections

* Some notes about passphrases

* Removed redundant text

* Update GETTING_STARTED.md

Minor word changes

---------

Co-authored-by: Maria Dimitrova <maria.dimitrova@csc.fi>
Co-authored-by: Maria Dimitrova <maria.dimitrova@helsinki.fi>

Author: 3 people

CONTRIBUTING.md

@@ -180,7 +180,7 @@ Pull requests can be created as follows:
 
 See the [FAQ](FAQ.md#how-can-i-preview-my-edits) for how to preview the Docs CSC website locally using MkDocs.
 
-A newbie-friendly guide on how to set up the necessary tools on Windows is available [here](WINDOWS.md).
+A newbie-friendly guide on how to set up the necessary tools on Windows is available [here](GETTING_STARTED.md).
 
 ## Building the website using the included Dockerfile