Move modelio into-cps desktop application related stuff

@CThuleHansen

# problem
"Modelio into-cps application" stuff is very specific and only relevant to that combination of tools.

https://into-cps-association.github.io/systemmodelling/

# proposal

move install instruction to:
https://into-cps-association.readthedocs.io/projects/desktop-application/en/latest/integrations.html#modelio


And mention the tool in general into-cps docs


Start by locating the current Modelio installation instructions in the documentation linked from the issue, then review the desktop-application integrations page and the general INTO-CPS documentation. Move the Modelio-specific installation material to the integrations page and add a general mention in the main documentation; done means both references are accurate and the old location no longer contains the detailed instructions.

Written by the indexing model from the issue text.