Write a migration guide (from other simulator)

[lukicdarkoo]

Here is a very nice migration guide example:
https://community.gazebosim.org/t/migration-from-gazebo-classic-to-ignition-gazebo/805
Besides the migration documentation, they also have case-studies.

I believe we should make something similar.

[omichel]

Yes, we should add such a migration guide to the wiki pages.