Added some Python documentation

python/README.md

@@ -0,0 +1,63 @@
+# Python bindings for the OPM-common module of the Open Porous Media project.
+
+## To compile with python support:
+
+- Add the cmake flags `-DOPM_ENABLE_PYTHON=ON` and `-DOPM_INSTALL_PYTHON=ON`
+- Optionally add prefix `-DCMAKE_INSTALL_PREFIX=/opt/opm` to install outside
+  the standard distro directories
+- Optionally specify python binary `-DPython3_EXECUTABLE=/home/user/miniconda3/envs/rkt/bin/python3`
+  if you don't want to use the system python, e.g. use a python from `pyenv` or from a `conda` environment
+
+### Sample compilation on linux:
+
+```bash
+#! /bin/bash
+
+flags="-DPython3_EXECUTABLE=/home/hakon/miniconda3/envs/rkt/bin/python3 -DOPM_ENABLE_PYTHON=ON -DOPM_INSTALL_PYTHON=ON -DCMAKE_INSTALL_PREFIX=/opt/opm"
+for repo in opm-common opm-grid opm-models opm-simulators
+do
+    cd "$repo"
+    mkdir -p build
+    cd build
+    cmake  $flags ..
+    make -j8
+    sudo make install
+    cd ..
+    cd ..
+done
+```
+
+Then you should be able to use the module from a Python script. If you installed in
+a non-standard directory by specifying `-DCMAKE_INSTALL_PREFIX` you may need to set the
+`PYTHONPATH` environment variable before running your Python script, for example:
+
+```bash
+$ PYTHONPATH=/opt/opm/lib/python3.11/site-packages python3 spe1case1.py
+```
+
+and `spe1case1.py` could be:
+
+```python
+import os
+from opm.simulators import BlackOilSimulator
+from opm.io.parser import Parser
+from opm.io.ecl_state import EclipseState
+from opm.io.schedule import Schedule
+from opm.io.summary import SummaryConfig
+
+os.chdir("SPE1CASE1")
+deck  = Parser().parse('SPE1CASE1.DATA')
+state = EclipseState(deck)
+schedule = Schedule( deck, state )
+summary_config = SummaryConfig(deck, state, schedule)
+unit_system = deck.active_unit_system()
+
+sim = BlackOilSimulator(deck, state, schedule, summary_config)
+sim.step_init()
+sim.step()
+poro = sim.get_porosity()
+poro = poro *.95
+sim.set_porosity(poro)
+sim.step()
+sim.step_cleanup()
+```