docs(ndb): Update README and CONTRIBUTING documentation

Author: chalmerlowe

packages/google-cloud-ndb/CONTRIBUTING.rst

@@ -24,7 +24,7 @@ In order to add a feature to ``python-ndb``:
   documentation (in ``docs/``).
 
 - The feature must work fully on the following CPython versions:
-  3.9, 3.10, 3.11, 3.12, 3.13 and 3.14 on both UNIX and Windows.
+  3.10, 3.11, 3.12, 3.13 and 3.14 on both UNIX and Windows.
 
 - The feature must not add unnecessary dependencies (where
   "unnecessary" is of course subjective, but new dependencies should
@@ -259,14 +259,12 @@ Supported Python Versions
 
 We support:
 
--  `Python 3.9`_
 -  `Python 3.10`_
 -  `Python 3.11`_
 -  `Python 3.12`_
 -  `Python 3.13`_
 -  `Python 3.14`_
 
-.. _Python 3.9: https://docs.python.org/3.9/
 .. _Python 3.10: https://docs.python.org/3.10/
 .. _Python 3.11: https://docs.python.org/3.11/
 .. _Python 3.12: https://docs.python.org/3.12/

packages/google-cloud-ndb/README.md

@@ -30,14 +30,14 @@ GA
 
 Our client libraries are compatible with all current [active][3] and [maintenance][4] versions of Python.
 
-Python >= 3.9
+Python >= 3.10
 
 [3]: https://devguide.python.org/devcycle/#in-development-main-branch
 [4]: https://devguide.python.org/devcycle/#maintenance-branches
 
 ### Unsupported Python Versions
 
-Python <= 3.8
+Python <= 3.9
 
 If you are using an [end-of-life][5]
 version of Python, we recommend that you update as soon as possible to an actively supported version.