DOC: add how to use built-in annotation formats

[NickleDave]

trafficstars

with demos that are tested, e.g. using TextGrid and Audacity datasets

I get the feeling people are now assuming they have to convert to 'simple-seq'

Also we should have the "naming convention" language on this page probably? and then link to it on the "how to use my own format" page. Also would be good to autopopulate this page with a list of the built-in formats from crowsetta

[NickleDave]

Should probably also change main how-to page so it says something like "if you're using a common format like Praat TextGrid or Audacity LabelTracks, it's already built-in; follow this how-to. If your annotation format is not built-in, then follow this how-to instead"