Add documentation on adding your logo

[cmungall]

We currently use depicted_by to allow people to include a logo, see http://obofoundry.github.io/ontology/obi.html

• Should a different property be used? Any semweb vocab have a property for logo?
• We should make it clear that the URL must resolve to actual image
• We should have guidelines on size (or dynamically resize?) - see #70

[nlharris]

did this get done?

[nlharris]

This does seem like a good thing to do -- maybe a potential volunteer activity?

[matentzn]

Yes, but anyone can do it, does not need a technical person.