"Installing" docs: Canopy distribution is EOL

[Kadabash]

In the Installing section of the documentation, Canopy is listed as a scientific Python distribution for Windows.
However, Canopy seems to have reached end-of-life (see its download page and an announcement by Enthought). There seems to be an alternative called "EDM", though the Matplotlib documentation should probably not refer to a product that is no longer available.

I hope this is the correct repository to report this.

[timhoffm]

Thanks for the note! This has already been addressed in #15652 and will take effect in the 3.3.0 docs.