add ttl syntax to format variant page

[shawntanzk]

For https://oboacademy.github.io/obook/explanation/owl-format-variants/#overview-of-the-relevant-concepts it would probably be useful to add ttl syntax in there too - I would do it, but I'll be honest, I barely have a grasp on this >.< will try to if I find some time to read up about it and all - just wanted to open a ticket to suggest in case anyone can do a quick addition

[cthoyt]

@shawntanzk turtle is a serialization format for RDF - so this is sort of covered already. Maybe it can be made clear that there are several flavors of serialization formats (turtle, n3, even JSON-LD) that can represent RDF