update 'Models' links in README (#4475)

* update 'Models' links in README

* tweak

Author: epwalsh

README.md

@@ -30,12 +30,13 @@
 - [Website](https://allennlp.org/)
 - [Guide](https://guide.allennlp.org/)
 - [Forum](https://discourse.allennlp.org)
-- Documentation ( [latest](https://docs.allennlp.org/latest/) | [stable](https://docs.allennlp.org/stable/) | [master](https://docs.allennlp.org/master/) )
+- [Documentation](https://docs.allennlp.org/) ( [latest](https://docs.allennlp.org/latest/) | [stable](https://docs.allennlp.org/stable/) | [master](https://docs.allennlp.org/master/) )
 - [Contributing Guidelines](CONTRIBUTING.md)
-- [Pretrained Models](https://github.com/allenai/allennlp-models/blob/master/allennlp_models/pretrained.py)
+- [Officially Supported Models](https://github.com/allenai/allennlp-models)
+  - [Pretrained Models](https://github.com/allenai/allennlp-models/blob/master/allennlp_models/pretrained.py)
+  - [Documentation](https://docs.allennlp.org/models/) ( [latest](https://docs.allennlp.org/models/latest/) | [stable](https://docs.allennlp.org/models/stable/) | [master](https://docs.allennlp.org/models/master/) )
 - [Continuous Build](https://github.com/allenai/allennlp/actions)
 - [Nightly Releases](https://pypi.org/project/allennlp/#history)
-- [Officially Supported Models](https://github.com/allenai/allennlp-models)
 
 ## Getting Started Using the Library