deprecated atmo channel

[Reimar Bauer]

Anaconda packages also using conda-forge for automated builds and has deprecated their own service.

And we will long term not doing ourselfs others than conda-forge builds for OSX we completly move our builds to the conda-forge service.

-c conda-forge is mandatory

documentation needs fixes

[Reimar Bauer]

Merged in ReimarBauer/mss (pull request #114)

docs: deprecated atmo channel removed, fixes #86

→ <<cset e1c1264e9f5a>>