Explain how the front page evaluation works

[brson]

Folks might be confused that it's running on the web.

Either put a link to an explanation under the editor or perhaps link to play.rust-lang.org and explain there.

[thestinger]

I think it would make sense to link from the front page to http://play.rust-lang.org/, and then http://play.rust-lang.org/ can have a link to the source code repository.

[SergioBenitez]

Would adding a small "open external" icon next to the result that, when clicked, opens up the playpen with the code already in place suffice?

[steveklabnik]

@SergioBenitez I like that.

[fhahn]

It seems like this issue was fixed with rust-lang/prev.rust-lang.org#35 which adds a button to playpen as described by @SergioBenitez above. Can this issue can be closed?