Add missing GenericName to simutrans.desktop

[m.vanderwulp]

I have a simple request:
Please add "GenericName=Transportation Simulation Game" in the simutrans.desktop file.

Rationale:

I usually prepare simutrans for packaging for OpenSUSE at https://build.opensuse.org/package/show/games/simutrans .
Recently, I received this message:
https://news.opensuse.org/2024/11/11/streamlining-translations/.
To make a long story short: The OpenSUSE people want to save effort by using the upstream (i.e. your) simutrans.desktop file, instead of adapting it.
There are no upstream translations for simutrans (in this file), so there is no problem, except that simutrans is missing the "GenericName" entry in this file.
Currently, in the package build process for OpenSUSE, we add: "GenericName=Transportation Simulation Game".
The presence of the GenericName is not obliged according https://specifications.freedesktop.org/desktop-entry-spec/latest/recognized-keys.html#id-1.7.6, but OpenSUSE uses it:
This text can be seen in the OpenSUSE UI in the main menu - see screenshot.

Once this is done, I can remove the "%suse_update_desktop_file" from the "simutrans.spec".

[Yona-TYT]

https://github.com/simutrans/simutrans/pull/4

I have opened a request.

[prissi]

We cannot take pull requests for simutrans executable as the master files are in the svn. So we only take patch files. But this was trivial, so I added it manually to the svn.