Fix/backend install

[tomalrussell]

Mainly for the notes on installing a python environment:

pip install . installs the backend package as defined by the pyproject.toml, and checks for its dependencies and installs them if needed

pip install -e . does an editable install, so changes in the source python files are directly reflected in the environment without needed to reinstall (still need to restart the uvicorn server)

pip install -e .[dev] includes the "dev" group of optional dependencies.

[mz8i]

This seems to work alright, so I'm assuming what I was doing wrong was running pip install . rather than pip install -e .[dev]...?

See just the one comment/question regarding docs and activate path, otherwise good to merge!

[mz8i]

Actually, I now checked again with pip install . and the dependencies also got installed, which is slightly surprising because they didn't before. I'm thinking maybe it was originally a problem with using some older version of pip that didn't support installing from pyproject.toml (even though I thought I'd checked for the right version).

In any case, the installation now works correctly when following the readme, which is most important!