Add XLM-V to Model Doc
Hi,

as discussed in #21330 it would be good to have an extra entry for the new XLM-V model in the Model Doc.

This PR adds it with some additional information about the model and conducted experiments with it.
_The documentation is not available anymore as the PR was closed or merged._<|||||>CI is failing, I'm going to read the Flan-T5 PR (https://github.com/huggingface/transformers/pull/19892) to see how it should be done!<|||||>You just need to add the model type (same as what you picked for the page in the doc) and name in the configuration_auto file. The PR you mention also does it :-) <|||||>Failures are unrelated to this PR so merging!