Show alternate install options on website

[withoutboats]

https://rustup.rs tries to figure out what OS you are visiting from, and show appropriate instructions on installation. Sometimes, though rustup.rs is wrong - for example, if you are using anti-fingerprinting software, your browser might return an inaccurate response causing us to believe you are running a different OS than you are.

We should support an option on the main page to switch it to display the installation instructions for other operating systems.

[jelford]

I could take this; I will have some time this week to put something together. I'm thinking of button at the bottom that says something like:

I think you're running on $platform, but if not, <here's> the full list.

... which would just switch to #platform-instructions-default. It could maybe show text like #platform-instructions-unknown (not exactly the same) below?

For what it's worth, as a NoScript user I see the default screen, and I just assumed that's what everyone saw; I never saw anything wrong with it.

[jelford]

I didn't get a chance to look at this while I was on holiday, and I don't think I'll be able to get to it now. If someone else wants to pick it up, that would seem sensible.

[senden9]

I added a pull request that pick that issue up. See #1300.