docs: Add conda-forge install details to README

[matthewfeickert]

• Add conda-forge badge to README.
  • c.f. https://github.com/conda-forge/pyhepmc-feedstock
• Add conda-forge install instructions to README.

[HDembinski]

Thank you, this is great, but if you want to change pip install to python -m pip install as well, please do that everywhere in the readme

[matthewfeickert]

but if you want to change pip install to python -m pip install as well, please do that everywhere in the readme

Sounds good. Will do later today. 👍

[matthewfeickert]

@HDembinski Should be resolved now:

$ git grep "pip" -- README.rst
README.rst:31:   python -m pip install pyhepmc
README.rst:35:However, building from source is also easy. External software is not required. Just download the repository with ``git clone --recursive`` and run ``python -m pip install -v -e .``.

[HDembinski]

Great, thank you very much.