Update comment line sentence

// join a site to a hubsite
to
// separate a site from a hubsite

docs/sp/hubsites.md

@@ -125,6 +125,6 @@ import { sp } from "@pnp/sp";
 import "@pnp/sp/sites";
 import "@pnp/sp/hubsites/site";
 
-// join a site to a hubsite
+// separate a site from a hubsite
 await sp.site.unRegisterHubSite();
 ```