[Docs] Model_doc structure/clarity improvements (#26876)

* first batch of structure improvements for model_docs

* second batch of structure improvements for model_docs

* more structure improvements for model_docs

* more structure improvements for model_docs

* structure improvements for cv model_docs

* more structural refactoring

* addressed feedback about image processors

docs/source/en/model_doc/xlm-prophetnet.md

@@ -36,7 +36,7 @@ Zhang, Ming Zhou on 13 Jan, 2020.
 
 XLM-ProphetNet is an encoder-decoder model and can predict n-future tokens for "ngram" language modeling instead of
 just the next token. Its architecture is identical to ProhpetNet, but the model was trained on the multi-lingual
-"wiki100" Wikipedia dump.
+"wiki100" Wikipedia dump. XLM-ProphetNet's model architecture and pretraining objective is same as ProphetNet, but XLM-ProphetNet was pre-trained on the cross-lingual dataset XGLUE.
 
 The abstract from the paper is the following:
 
@@ -52,11 +52,7 @@ state-of-the-art results on all these datasets compared to the models using the
 
 The Authors' code can be found [here](https://github.com/microsoft/ProphetNet).
 
-Tips:
-
-- XLM-ProphetNet's model architecture and pretraining objective is same as ProphetNet, but XLM-ProphetNet was pre-trained on the cross-lingual dataset XGLUE.
-
-## Documentation resources
+## Resources
 
 - [Causal language modeling task guide](../tasks/language_modeling)
 - [Translation task guide](../tasks/translation)