DOC: List min. Python version for Matplotlib 3.10

Author: timhoffm

doc/devel/min_dep_policy.rst

@@ -115,6 +115,7 @@ specification of the dependencies.
 ==========  ========  ======
 Matplotlib  Python    NumPy
 ==========  ========  ======
+`3.10`_     3.10      1.23.0
 `3.9`_      3.9       1.23.0
 `3.8`_      3.9       1.21.0
 `3.7`_      3.8       1.20.0