Minor tweaks to CHANGELOG and README prior to putting out a release candidate

Author: tleonhardt

CHANGELOG.md

@@ -1,4 +1,4 @@
-## 3.0.0 (TBD, 2025)
+## 3.0.0 (October TBD, 2025)
 
 ### Summary
 

README.md

@@ -27,7 +27,8 @@ when using cmd.
 
 > :warning: **cmd2 is now "feature complete" for the `2.x` branch and is actively working on the
 > 3.0.0 release on the `main` branch. New features will only be addressed in 3.x moving forwards. If
-> need be, we will still fix bugs in 2.x.**
+> need be, we will still fix bugs in 2.x. A beta version, 3.0.0b2, is available for testing and we
+> would appreciate feedback.**
 
 ## The developers toolbox