Fix installation with Conda

[aufdenkampe]

Following today's new Installation instructions From Source using Conda, I got this error:

(babelizer) aaufdenkampe@ExcaliburMac2 babelizer % conda install --file=requirements.txt -c conda-forge

CondaValueError: could not parse 'importlib-resources; python_version < '3.12'' in: requirements.txt

It worked using pip: $ pip install -e .

[mcflugen]

@aufdenkampe Although conda understands the most basic pip requirements file, it doesn't understand markers or specifiers—as we have in this file.

We should probably just remove the conda installation option from the instructions for installing from source.

[aufdenkampe]

That works for me!