Add more documentation on how to explore output

[cmungall]

In

• #185

We add obojson output, which can be fed into obographviz - but we don't really explain any of this on the README

Also just general docs on how to explore the different output files

[nlharris]

I don't seem to have any privileges on this repo.

Can this be closed?

[balhoff]

We can leave it open for now. I'm in the middle of a big overhaul of boomer, which may or may not pan out. It would impact how the output is used.