Not sure why you want a macro. A date field will do this.
You could save it as AutoText and attach a keyboard shortcut if you want.
Using Date Fields in Microsoft Word
In Word 2013, the quickest way to the customize keyboard dialog is through the customize the ribbon dialog. Right-click on the ribbon, choose that, then click on the button at the bottom to customize the keyboard.
You can use the same dialog to add a keyboard shortcut to a macro.
The keyboard shortcut should be stored in the same template as the building block (AutoText) or macro. This can be a
Global Template, other than the normal template, or could be the normal template.