bump suggested version

Author: jepler

README.rst

@@ -27,7 +27,7 @@ This library depends on:
 * `Adafruit CircuitPython <https://github.com/adafruit/circuitpython>`_
 
 Note that some CircuitPython core changes were needed to support udecimal.
-These will be in upcoming release 6.0.0.alpha-4.
+Please use CircuitPython 6.0.0-rc.1 or newer with udecimal.
 
 The library also runs on desktop Python3, and should give numerically identical
 results across all platorms.