Add linke to allennlp-models in README
- [Pretrained Models](https://github.com/allenai/allennlp-hub/blob/master/allennlp_hub/pretrained/allennlp_pretrained.py)
- [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)
## Package Overview
