Feature enhancement: prompt the user to use ⌘-c when copying the clone project URI

Currently on OS X hitting the copy to clipboard button simply highlights the input which contains the clone URI, with the expectation that the user will know to copy the link manually themselves. A tooltip should be shown advising the user that they must manually copy this text otherwise the implication is that clicking the button puts the URI on the clipboard.

It's possible that since the forthcoming versions of Safari offer the ability to put text on the clipboard this won't be an issue long enough to be worth fixing.