docs/guides/beta.md: explain dasharo beta

Signed-off-by: Michał Kopeć <[email protected]>

Author: mkopec

docs/guides/beta.md

@@ -5,6 +5,15 @@
 This document explains the Dasharo Beta update channel, how to enroll in it and
 how to downgrade back to stable.
 
+The Dasharo Beta update channel provides pre-release binaries ready for public
+testing by a group of beta testers. These binaries are not thoroughly tested,
+but provide a preview of future features and enhancements.
+
+## Joining the beta tester group
+
+Please follow the steps [here](https://docs.dasharo.com/ways-you-can-help-us/#join-dasharo-beta-testing-group)
+to join the Dasharo Beta Testing group.
+
 ## Enabling
 
 To enable Dasharo Beta updates, execute this command in a terminal: