Update Python version requirements in Sphinx docs (3.10+/PyPy 3.11+)

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: vthorsteinsson

doc/index.rst

@@ -10,7 +10,7 @@ Welcome to Greynir
 *Til að gagnast sem flestum er skjölun Greynis á ensku. - In order to serve
 the widest possible audience, Greynir's documentation is in English.*
 
-Greynir is a Python >= 3.9 package for **working with Icelandic text**,
+Greynir is a Python >= 3.10 package for **working with Icelandic text**,
 including parsing it into **sentence trees**, finding **lemmas**,
 inflecting **noun phrases**, assigning **part-of-speech tags** and much more.
 

doc/installation.rst

@@ -6,7 +6,7 @@ Installation
 Prerequisites
 -------------
 
-Greynir runs on **CPython 3.9** or newer, and on **PyPy 3.9**
+Greynir runs on **CPython 3.10** or newer, and on **PyPy 3.11**
 or newer (more info on PyPy `here <http://pypy.org/>`_).
 
 On GNU/Linux and similar systems, you may need to have ``python3-dev``