Mark wingspan-cursor as deprecated

In preparation for the 1.0 release and the goal of evangelizing cursors into react core, Danny and I agreed to rebrand to "react-cursor" and hosting at a github I control, so that during evangelism I can hot patch things in real time as needed during the discussions, add documentation, etc. That way I don't need push access on wingspan's fork. I'm iterating the cursor implementation very quickly so the fork is better in the other direction anyway.

As to the rebranding, I know of two people other than me and Wingspan using our cursors now, and there is confusion over which fork to use (mine or wingspans). So I've changed the name so that it will not be confused on google with this repo.

This PR brings you guys up to sync with my latest, additionally with an updated README.md with a link to dustingetz/react-cursor, so anybody tracking the wrong fork will eventually notice and update. In a couple weeks, the wingspan/wingspan-cursor repo should be made private so nobody will get confused, and when the dust settles after the evangelism period, wingspan can upgrade to dustingetz/react-cursor if appropriate and desired.

Note that this PR breaks backwards compatibility with the TMF.