Direct users to docs site for Mac instructions

[analogrelay]

Since there aren't really "dev" instructions any more (because there's just one version of DNVM for both branches), it seemed unnecessary to duplicate the changes I just made in aspnet/Docs here.

Fixes aspnet/homebrew-dnx#20

/cc @glennc @danroth27 @Eilon @DamianEdwards @muratg

[dnfclas]

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[muratg]

We have Linux and Windows installation instructions there as well. Should we remove those from here as well?

[analogrelay]

We could. Maybe just reduce the whole "getting started" section here down to a link to http://docs.asp.net/en/latest/getting-started/index.html

[tlk]

Would you consider adding a Docker section?

[Eilon]

@tlk the docs are all on GitHub as well - you can submit suggestions and PRs at https://github.com/aspnet/Docs/. There might already be some Docker stuff on there, so please do a search to see what might already be in progress.

[analogrelay]

I updated all of them to point to the docs site instructions. There are actually already some Docker instructions on the docs site so that should cover it (and feel free to update them with PRs to aspnet/Docs!)

[muratg]

Nice.