Add Windows as supported platform on conda-forge

[asjohnston-asf]

The isce3 package distributed via conda-forge at https://anaconda.org/channels/conda-forge/packages/isce3/overview currently lists supported platforms as:

linux-64
macOS-arm64
macOS-64 

Windows users currently receive an error when trying to install isce3 via conda-forge:

>conda install isce3
Retrieving notices: done
Channels:
 - conda-forge
Platform: win-64
Collecting package metadata (repodata.json): done
Solving environment: failed

PackagesNotFoundError: The following packages are not available from current channels:

  - isce3

Current channels:

  - https://conda.anaconda.org/conda-forge

To search for alternate channels that may provide the conda package you're
looking for, navigate to

    https://anaconda.org/

and use the search bar at the top of the page.