explicitly using conda-forge channel to help Windows installation

Author: eglerean

content/xarray.rst

@@ -49,7 +49,7 @@ We will first download a dataset similar to the example above to illustrate the
 
    If you have set up your ``python-for-scicomp`` environment yesterday or earlier, you need to install the packages ``netcdf4`` and ``pythia_datasets`` manually. You can do this by running the following command in your (JupyterLab) terminal: ::
 
-        conda install netcdf4 pythia-datasets
+        conda install netcdf4 pythia-datasets -c conda-forge
 
 Let us open a python shell and download a public dataset: ::