doc: added instruction for creating python env [ci-skip]

Author: jlerat

README.rst

@@ -11,6 +11,7 @@ What is pygme?
 
 Installation
 ~~~~~~~~~~~~
+- Create a suitable python environment. We recommend using `miniconda <https://docs.conda.io/projects/miniconda/en/latest/>`__ combined with the environment specification provided in the env_nriv_v2.yml file in this repository.
 - Install the `hydrodiy <https://github.com/csiro-hydroinformatics/hydrodiy>`__ package.
 - Download the `source code <https://github.com/csiro-hydroinformatics/pygme>`__ and run ``python setup.py install``.