Merge pull request cncf#826 from dims/update-mailing-list-and-slack-info

update mailing list and slack info

README.md

@@ -65,10 +65,17 @@ Here is a [Google calendar for all public CNCF events](https://goo.gl/eyutah). T
 
 ## Mailing List
 
-[email protected]: https://lists.cncf.io/g/cncf-toc
+Public mailing list for the CNCF TOC: [email protected]
 
-To join: https://lists.cncf.io/mailman/listinfo/cncf-toc
+The public mailing archive: https://lists.cncf.io/g/cncf-toc
 
+Details to join this public mailing list: https://lists.cncf.io/mailman/listinfo/cncf-toc
+
+In case you need to reach the CNCF TOC on sensitive issues, please email us at: [email protected]
+
+## Slack
+
+Public CNCF TOC channel: Join the [CNCF slack](https://slack.cncf.io/) and we are reachable at [#toc](https://cloud-native.slack.com/archives/C0MP69YF4). 
 
 ## Voting