Caveat about circuitpython support

Author: jepler

README.rst

@@ -22,13 +22,16 @@ Reduced version of the decimal library for CircuitPython
 
 Dependencies
 =============
-This driver depends on:
+This library depends on:
 
 * `Adafruit CircuitPython <https://github.com/adafruit/circuitpython>`_
 
-Please ensure all dependencies are available on the CircuitPython filesystem.
-This is easily achieved by downloading
-`the Adafruit library and driver bundle <https://circuitpython.org/libraries>`_.
+Note that some CircuitPython core changes are currently needed to support
+udecimal.  Until they are merged, you can use the artifacts from `the relevant
+pull request <https://github.com/adafruit/circuitpython/pull/3377>`_.
+
+The library also runs on desktop Python3, and should give numerically identical
+results across all platorms.
 
 Installing from PyPI
 =====================