docs: Update Readme for community support link

Replace link from NGINX community slack with community forum.

Closes #1044

Author: javorszky

README.md

@@ -593,9 +593,8 @@ docker buildx imagetools inspect nginx/nginx-prometheus-exporter:edge --format '
 ## Contacts
 
 We’d like to hear your feedback! If you have any suggestions or experience issues with the NGINX Prometheus Exporter,
-please create an issue or send a pull request on GitHub. You can contact us directly via <[email protected]> or on
-the [NGINX Community Slack](https://nginxcommunity.slack.com/channels/nginx-prometheus-exporter) in the
-`#nginx-prometheus-exporter` channel.
+please create an issue or send a pull request on GitHub. You can contact us directly via <[email protected]> or
+on the [NGINX Community Forums](https://community.nginx.org/).
 
 ## Contributing