x/playground: Inform users of run / format shortcuts

[NiloCK]

https://tour.golang.org/welcome/1 includes the helpful tips that shift+Enter runs the program, and ctrl+Enter runs the formatter.

These shortcuts exist also at play.golang.org, but are not discoverable.

What version of Go are you using (go version)?

play.golang.org

Does this issue reproduce with the latest release?

not applicable

What operating system and processor architecture are you using (go env)?

not applicable

[cagedmantis]

/cc @toothrot

[Deleplace]

Thank you @NiloCK , I didn't know about Shift+Enter in the Playground to run the code, so I was left puzzled with Ctrl+Enter that would only format it, and I was about to create a bug specifically to ask for a keyboard shortcut for "Run"...

Now I realize that "shift-enter" is in the tooltip of the "Run" button at https://go.dev/play/ (I don't know if it was there all along, or a recent addition).

Yes definitely using the mouse for this, like I did, is suboptimal, and it would be very useful imo to make this information more prominent.