Update project page and README to specify this also works for D6 nodequeues

I just installed this module on a D8 test site where I'm migrating from a D6 site that made *heavy* use of nodequeues. I'm extremely happy to report that it all Just Worked(tm). Flawlessly! All the queues were created, all the entity references were populated correctly, in the right order, etc. YAY! Thanks so much!!

Perhaps it's worth updating the project page (and README) to indicate that it will work for D6 nodequeues as well?

Thanks again!

Cheers,
-Derek