[PNM][util] Add version requirements for extract_ pore_network and openpnm2dgf script

dumux/porenetwork/util/README.md

@@ -8,4 +8,7 @@ To try the script, there is a sample `raw` binary image in the folder. For testi
 
 which generates `sample.dgf`.
 
+Python versions tested for the above mentioned python scripts:
+- Python 3.10.6
+
 TODO: These steps should be tested automatically in the future in a CI setup with `porespy` and `OpenPNM` installed.

dumux/porenetwork/util/requirements.txt

+# SPDX-FileCopyrightInfo: Copyright © DuMux Project contributors, see AUTHORS.md in root folder
+# SPDX-License-Identifier: CC0-1.0
+
+porespy~=2.1.0
+openpnm~=2.8.2
+loguru~=0.6.0