Add a section of pre-trained embeddings in README (facebookresearch#11)

Summary:
- [x] Docs change / refactoring / dependency upgrade
- [ ] Bug fix (non-breaking change which fixes an issue)
- [ ] New feature (non-breaking change which adds functionality)
- [ ] Breaking change (fix or feature that would cause existing functionality to change)

Add a new section which contains pre-trained embeddings.

- [x] The documentation is up-to-date with the changes I made.
- [x] I have read the **CONTRIBUTING** document and completed the CLA (see **CONTRIBUTING**).
- [x] All tests passed, and additional code has been covered with new tests.
Pull Request resolved: facebookresearch#11

Differential Revision: D14721339

Pulled By: adamlerer

fbshipit-source-id: 0c47ef8b48146b9b5fe2b4eca69c7e1e40a8790f

README.md

@@ -151,6 +151,10 @@ This will create the `joined_embeddings.tsv` file, which is a text file where ea
 
 More information can be found in [the full documentation](https://torchbiggraph.readthedocs.io/).
 
+## Pre-trained embeddings
+
+We trained a PBG model on the full [Wikidata](https://www.wikidata.org/) graph, using a [translation operator](https://torchbiggraph.readthedocs.io/en/latest/scoring.html#operators) to represent relations. It can be downloaded [here](https://dl.fbaipublicfiles.com/torchbiggraph/wikidata_translation_v1.tsv). We used the truthy version of data from [here](https://dumps.wikimedia.org/wikidatawiki/entities/) to train our model. The model file is in TSV format as described in the above section. Note that the first line of the file contains the number of entities, the number of relations and the dimension of the embeddings, separated by tabs. The model contains 78 milion entities, 4,131 relations and the dimension of the embeddings is 200.
+
 ## Citation
 
 To cite this work please use: