Update docs (FAQ) on WPML compatibility

[straube]

The plugin docs have to be updated to include a Q&A on compatibility with WPML. This is a recurrent topic both here on Github and on WP Support Forums. Below there is a response I gave recently that could be used as a starting point for this doc update.

This plugin is not compatible with WPML nor any other plugin that relies on domain changes to work. This is a known issue for a while but there is no fix on the way. You can follow some discussions in here.

Yet, in case you simply need to have 1 domain per language, WPML handles that for you alone. There is no need to use Multiple Domain plugin. You just have to set it to use language in domains.

If you want more than one domain per language, this is an old tutorial from WPML that might work for you.

Originally posted by @straube in https://github.com/straube/multiple-domain/issues/73#issuecomment-589742824