Update outdated instructions in scripts/generate_pip_deps_from_conda.py

[MarcoGorelli]

It says

Usage:

    Generate `requirements-dev.txt`
    $ ./conda_to_pip

    Compare and fail (exit status != 0) if `requirements-dev.txt` has not been
    generated with this script:
    $ ./conda_to_pip --compare

but it should be

Usage:

    Generate `requirements-dev.txt`
    $ python scripts/generate_pip_deps_from_conda.py

    Compare and fail (exit status != 0) if `requirements-dev.txt` has not been
    generated with this script:
    $ python scripts/generate_pip_deps_from_conda.py --compare

No need to ask if you can work on this, feel free to just submit a PR

[dishak331]

I would like to work on this

[dishak331]

https://github.com/pandas-dev/pandas/pull/36506

[MarcoGorelli]

I would like to work on this

This is taken, but there's lots of other issues you can contribute to if you like!