Fix install docs: minimum Python version is 3.10

Update docs/install/install_instructions.md to match
NRN_MINIMUM_PYTHON_VERSION in CMakeLists.txt.

Fixes #3803

Author: Grok

docs/install/install_instructions.md

@@ -214,7 +214,7 @@ In order to build NEURON from source, the following packages must be available:
 
 The following packages are optional (see build options):
 
-- Python >=3.8 (for Python interface)
+- Python >=3.10 (for Python interface)
 - Cython (for RXD)
 - MPI (for parallel)
 - X11 (Linux) or XQuartz (MacOS) (for GUI)