use borgbackup.org as main site

the github site is linked via project_urls -> Source Code

setup.cfg

@@ -2,7 +2,7 @@
 name = borgbackup
 author = The Borg Collective (see AUTHORS file)
 description = Deduplicated, encrypted, authenticated and compressed backups
-url = https://github.com/borgbackup/borg
+url = https://borgbackup.org
 keywords =
   backup
   borgbackup