Submit button works with CMD + Enter but no hint for that!

[mdmag]

At the moment, Submit Button isn't working with hitting "Enter" only because the user might hit "Enter" thinking that he will go to the next block but the submission will be processed unintentionally. That's why Submit is working with combination of CMD + Enter key together and that's great at the moment but there is no hint for the user to let him know he can process the submission using those keys.
The hint should be different according to the operating system. For mac users, it should be CMD + Enter and for any other PC operating system, it should be ⊞ Win + Enter. For any other mobile operating system, there would be no hint mainly.