[documentation] Add troubleshooting section for installation, e.g. venv and anaconda issues (nrniv -python and mpiexec not working)

[salvadord]

The mpi issue with nrniv -python was indeed due to conflicts between anaconda and venv
the issue is more general and results in an error if you run nrninv -python and then from neuron import h

it’s likely that this is gonna be an issue for many people since anaconda quite popular (and actually recommended by NEURON website)
eg see the end of this tutorial, they had same issue: https://nickgeorge.net/programming/NEURON-neuronal-modeling-software-and-python-with-virtual-environments/

I solved it by using brew install open-mpi but then also had to change paths inside the venv (add to bashrc or bin/activate):

export PYTHONPATH=/u/salvadord/venvs/neuron78/lib/python3.8/site-packages:$PYTHON
export PATH=/usr/local/bin/:$PATH

[dhasegan]

You might also want to reference tkinter dependency for Mac.
Here was my solution for installing it for 3.7 through pyenv from StackOverflow (https://stackoverflow.com/questions/60469202/unable-to-install-tkinter-with-pyenv-pythons-on-macos/60469203#60469203)

[salvadord]

@jchen6727 I think this is kind of addressed with the new installation instructions you added?

[jchen6727]

those installation instructions were for Windows -> WSL, and then entirely within a Conda environment on Rocky Linux. I think this will just be a reoccurring issue of varying significance as new environments occur. Should we just close for now and just reopen as necessary for specific OS / (widely used) hardware?

On that note, I managed to pull off the installation of mpi, neuron and python without using brew after I got my MacBook, so it may be possible that everything can be handled through Conda at this point, though picking the right mpi binary will still be an issue per OS per hardware.