Git Extensions documentation improvements

[gerhardol]

Do you want to request a feature or report a bug?
feature

What is the current behavior?
The Git Extensions documentation needs improvements.

If the current behavior is a bug, please provide the steps to reproduce and if possible a minimal demo of the problem.
The GE doc was improved for 3.00 in #5693 https://git-extensions-documentation.readthedocs.io/en/latest/

The doc is still out of date, some example:

• Some functionality added since 2013 is not described at all or not in detail
• Links to standard Git documentation should be added where needed
• Some restructuring should be done, for instance branches and modify Git History are both covering rebase to some extent

What is the expected behavior?
Better documentation

Environment you encounter the issue:

• Git Extensions 3.00.00.4433
• Build fca7cf2
• Git 2.20.1.windows.1
• Microsoft Windows NT 10.0.17134.0
• .NET Framework 4.7.3260.0
• DPI 96dpi (no scaling)

Did this work in previous version of GitExtensions (which)?
In 2013 the doc was up-to-date

[vbjay]

• Remove Linux references
  

[gerhardol]

Remove Linux references

Opened a wip PR for minor issues like this, no need for separate issues/PRs
gitextensions/GitExtensionsDoc#91