Suggestion to change the conda installation instructions

[ranpelta]

Hi, the instructions to install 'fiona>=1.5' 'rasterio>=1.2.6', and 'h5py>3.7.0' on Windows via conda did not work for me.
I instead used the conda-forge for that, so maybe you can change that in the README file.

This is what worked for me:
conda install -c conda-forge "fiona>=1.5" "rasterio>=1.2.6"
conda install -c conda-forge "h5py>3.7.0"