added gene to pathway files for reactome ingest

[kevinschaper]

Looks great! There are a couple of extra steps that probably aren't in the docs yet that this needs:

• Adding a stanza in download.yaml with the url for the file to download,
• Adding the ingest to the list within monarch_ingest/ingest_pipeline.py

edit to add: Oops, 3 things, also the documentation in docs/ingests