[SLL] How do you make a patch file?

[Clifford Snow]

I want to send in a fix to a bug in the gnome-applets.  Instead of
sending in the entire file, how do you create a patch file that a
maintainer could just apply to the source code?  

In this case it is the Location.xml file that has one line wrong. So
instead of displaying a forecast for Seattle in the Weather applet, it
just gives a blank page.  I went ahead and sent in the entire file, but
it would make more sense to just send in a patch. 

Thanks,
Clifford