[doc] bart doc examples aren't for bart
If you look at the very end of this section https://huggingface.co/transformers/model_doc/bart.html#transformers.BartForConditionalGeneration.generate
there are 5 examples of using `generate` none of which is for BART. Is this an accidental copy-n-paste issue and they should just be removed? 

There are examples of generate for BART in the pre-amble of the class:
https://huggingface.co/transformers/model_doc/bart.html#bartforconditionalgeneration


Those examples are from the `generate` method doc which is a generic method shared by all generative models.<|||||>Thank you, @patil-suraj. Indeed, since `BartForConditionalGeneration` uses super-super class's `generate` it ends up having that generic signature in its docs.

What I'm trying to say is that these example are confusing to the user since not only they are irrelevant to someone trying to use BART, there isn't even an example of using bart in that part of the doc (there is one earlier in the class signature).

e.g. they don't show up in other similar classes which have `generate`
https://huggingface.co/transformers/model_doc/t5.html#t5forconditionalgeneration
https://huggingface.co/transformers/model_doc/marian.html
but there they have their own `generate` methods, so this doesn't happen.

I'm trying to flag a poor user experience and asking whether perhaps there is a better way to do it?

One possible suggestion:
- remove the 5 examples from `generate` at https://github.com/huggingface/transformers/blob/master/src/transformers/generation_utils.py#L215
- replace with a note - see this class' pre-amble documentation for examples.<|||||>feel free to send a PR deleting generate here
https://github.com/huggingface/transformers/blob/master/docs/source/model_doc/bart.rst#L35
<|||||>Thank you, Sam.
https://github.com/huggingface/transformers/pull/6659

