Add recommendations for channel setup on created environments

Our env script creates a new installable conda environment that allows users to create an conda environment from scratch using the right channels.

After the creation, the user is left w/o the channels so executing a mamba install bla would try to install bla from anaconda instead of conda-forge. To avoid this, it would be good to have a set of instructions that recommend adding conda-forge and other channels to the search space of the newly created space.