Installation instructions on README.md

[akeapen]

Requires update README.md from:

cd torchsig
pip install -r requirements.txt
pip install .

to...

cd torchsig
pip install -e .

in order to conform to installing dependencies via pyproject.toml

[gvanhoy]

I don't think we want to encourage an editable install by default, but no longer needing to install the requirements in the old way should be removed -- thanks.