Comment that it may vary by board

Author: tannewt

docs/templates/unsupported_in_circuitpython.inc

@@ -1,8 +1,8 @@
 .. warning::
 
    Though this MicroPython-based library may be available for use
-   in CircuitPython, it is unsupported and its functionality may change
-   in the future, perhaps significantly.
+   in some builds of CircuitPython, it is unsupported and its functionality
+   may change in the future, perhaps significantly.
    As CircuitPython continues to develop, it may be changed
    to comply more closely with the corresponding standard Python library.
    You will likely need to change your code later if you rely