Update docs and workflows to use `cob-edit.tsv`

[jamesaoverton]

The src/ontology/cob-edit.tsv is now the source-of-truth for all our COB terms. We generate cob-edit.owl from it, and we should no longer be committing cob-edit.owl to the repo

• document cob-edit.tsv, how it works, the meanings of the columns, how to edit, what scripts / Make tasks to run, etc.
• add src/ontology/cob-edit.owl and src/ontology/cob.tsv to .gitignore because they are now generated from cob-edit.tsv by a script done in a91255b
• change the trigger in .github/workflows/build.yml line 9 from 'src/ontology/**-edit.owl' to 'src/ontology/cob-edit.tsv'.