Add option to automatically add the file name to the commit message

I find it useful to indicate at the start of the commit message which file has been changed, so that commit summaries, such as on the github home page, indicate which file a message refers to.

If a single flie is being committed, it would be useful to have a button or option to insert the file name of the file being committed at the beginning of the message box to save me typing it each time.

For example, my last commit message read:

vertical-text, adjustments after running all tests on latest browser