Add Top-Level Page for Installer

[frankkopp]

Have a Installer section parallel to the SimBridge section

This is a temporary solution until we have restructured the navigation in general which will be required once the A380 will be added.

The Installer section should have a quick overview and howto-use page - could be simple as the Installer is really easy to use.
Import is a "KnowIssues / Troubleshooting" section to describe common issues based on the Discord issues which come up often.

[Valastiri]

If no one get's to this after I finish the failures PR -- I'll look into setting this up