Update README.md

Author: wsafonov

README.md

@@ -22,7 +22,12 @@ We take care of porting changes done in older supported MPS versions to the newe
 For details see [wiki](https://github.com/IETS3/iets3.opensource/wiki/Supported-MPS-Versions).
 
 ### What MPS versions are currently supported? 
-- MPS 2020.3 (branch: [master](https://github.com/IETS3/iets3.opensource/tree/master)) 
+- MPS 2021.1 (branch: [master](https://github.com/IETS3/iets3.opensource/tree/master)) 
+- MPS 2020.3 (branch: [maintenance/mps20203](https://github.com/IETS3/iets3.opensource/tree/maintenance/mps20203)) 
 - MPS 2020.2 (branch: [maintenance/mps20202](https://github.com/IETS3/iets3.opensource/tree/maintenance/mps20202)) 
 - MPS 2020.1 (branch: [maintenance/mps20201](https://github.com/IETS3/iets3.opensource/tree/maintenance/mps20201)) 
-- MPS 2019.3 (branch: [maintenance/mps20193](https://github.com/IETS3/iets3.opensource/tree/maintenance/mps20193))  
+
+## Community
+
+### Slack
+Ask your questions about KernelF and talk to other users and authors of the IETS3 language library on the public [Slack channel](https://jetbrains-mps.slack.com/archives/CBM449YG5)