remove mention of defunct googlegroup

README.md

@@ -13,10 +13,8 @@ replacement for NCURSES on existing systems.
 
 for more information, see [dankwiki](https://nick-black.com/dankwiki/index.php/Notcurses)
 and the [man pages](https://notcurses.com). in addition, there is
-[Doxygen](https://notcurses.com/html/) output. To subscribe to the
-[mailing list](https://groups.google.com/forum/#!forum/notcurses), send an email
-to [email protected] (the email contents don't matter). i wrote a coherent
-[guidebook](https://nick-black.com/htp-notcurses.pdf), which is available for
+[Doxygen](https://notcurses.com/html/) output.
+i wrote a coherent [guidebook](https://nick-black.com/htp-notcurses.pdf), which is available for
 free download (or [paperback purchase](https://amazon.com/dp/B086PNVNC9)).
 
 i've not yet added many documented examples, but [src/poc/](https://github.com/dankamongmen/notcurses/tree/master/src/poc)