KG2 README is Out of Date

[ecwood]

Just glancing at the README for a little bit, I saw that our README is out of date. For example, it doesn't say we use KEGG (nor is the Snakemake graphic correct) and it is likely out of date on UMLS/ontology sources. There are probably other issues with the README since I didn't look very long, but it would be a good idea to do a deep read of the file to correct errors.