Write down some installation details for OpenBSD

[irl]

before I forget. Maybe these end up in docs eventually.

Creating a virtualenv is a pain because Python is compiled with wxallowed. I've not checked if all the bitbot deps are happy to not have wx pages, but this is how Python is in ports by default so we have to deal with it. The easy way is to just use /usr/local for the venv because this is already mounted with wxallowed, /home is not.

As root:

pkg_add -x py3-virtualenv py3-pip libxslt libxml
mkdir /usr/local/bitbot_venv
chown user:user /usr/local/bitbot_venv

As user:

cd /usr/local/bitbot_venv
virtualenv-3 .
source bin/activate
cd /path/to/bitbot
export CPATH=/usr/include:/usr/local/include:/usr/local/include/libxml2:/usr/local/include/libxslt
pip install -r requirements.txt