Indicate that Python 3.10 is not supported (databricks#27)

Advise developers to use Python 3.7, 3.8, or 3.9 until databricks#26 is fixed.

Author: Jesse

README.md

@@ -11,7 +11,7 @@ You are welcome to file an issue here for general use cases. You can also contac
 
 ## Requirements
 
-Python 3.7 or above is required.
+A development machine running Python >=3.7, <3.10.
 
 ## Documentation