[Documentation] Documentation for Graphical compare feature is missing

[jthoene]

There is no part for the graphical compare feature in the documentation. A documentation for versioning system support for SCT is also missing.

[ghost]

A proper documentation for the versioning system support can be done after #2044 is resolved.

[tkutz]

We have something here: https://www.itemis.com/en/yakindu/state-machine/documentation/user-guide/edit_comparing_statecharts#edit_comparing_statecharts

But it is not super helpful I guess.