HELP-US: the label "PR-welcome" is now renamed to "help wanted"

following the new github "standard"

docs/HELP-US.md

@@ -17,9 +17,9 @@ down and report the bug. Or make your first pull request with a fix for that.
 
 ## PR-welcome
 
-In the issue tracker we occasionally mark bugs with
-[PR-welcome](https://github.com/curl/curl/labels/PR-welcome), as a sign that
-the bug is acknowledged to exist and that there's nobody known to work on this
+In the issue tracker we occasionally mark bugs with [help
+wanted](https://github.com/curl/curl/labels/help%20wanted), as a sign that the
+bug is acknowledged to exist and that there's nobody known to work on this
 issue for the moment. Those are bugs that are fine to "grab" and provide a
 pull request for. The complexity level of these will of course vary, so pick
 one that piques your interest.