Remove custom satis installation path from install instructions

[Ocramius]

Since packagist seems to be quite reliable, I don't see a reason to still suggest folks to point their composer.json definition at packages.zendframework.com

[froschdesign]

@weierophinney
Must be changed in the (old) manual files on the server and in all related blog posts. Or ignore it – the decision is up to you as a project maintainer / owner. 😉

[weierophinney]

This is the wrong repo at this point, and I don't think the current web repo mentions packages.zendframework.com at all. As such, closing this one.