docs: Add conda-forge install details to README

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

README.rst

@@ -9,6 +9,9 @@ A Pythonic wrapper for the `HepMC3 C++ library <http://hepmc.web.cern.ch/hepmc>`
 .. image:: https://badge.fury.io/py/pyhepmc.svg
   :target: https://pypi.org/project/pyhepmc
 
+.. image:: https://img.shields.io/conda/vn/conda-forge/pyhepmc.svg
+  :target: https://github.com/conda-forge/pyhepmc-feedstock
+
 .. image:: https://coveralls.io/repos/github/scikit-hep/pyhepmc/badge.svg?branch=main
   :target: https://coveralls.io/github/scikit-hep/pyhepmc?branch=main
 
@@ -21,10 +24,22 @@ HepMC3 has its own Python bindings. Why should you use these?
 
 **pyhepmc is easy to install**
 
-The command ``pip install pyhepmc`` just works on all common platforms. Since we publish binary wheels, you don't need to compile anything. Since we include the HepMC3 library, you don't need to install it separately either.
+The command
+
+.. code:: bash
+
+   python -m pip install pyhepmc
+
+just works on all common platforms. Since we publish binary wheels, you don't need to compile anything. Since we include the HepMC3 library, you don't need to install it separately either.
 
 However, building from source is also easy. External software is not required. Just download the repository with ``git clone --recursive`` and run ``pip install -v -e .``.
 
+``pyhepmc`` is also available on conda-forge
+
+.. code:: bash
+
+   conda install --channel conda-forge pyhepmc
+
 **pyhepmc is Pythonic, Numpy-friendy, and Jupyter notebook-friendly**
 
 pyhepmc is a hand-crafted mapping of C++ code to Python, `see documentation for details <https://scikit-hep.org/pyhepmc/reference.html>`_, while the official HepMC3 bindings are generated by a script. The pyhepmc API has been optimised for safety, usability, and efficiency by a human expert, something that an automatic tool cannot provide. pyhepmc brings these unique features: