changes to upstream sources/HOWTO patch
I've noticed that some packages contain a debian/patches-dir and I'm curious
how this works. I think I need to patch one of my packages myself so I'm
looking for some documentation. The Debian policy  does not really help
since the part about "changes to upstream sources" is quite short.
Can someone explain to me how to apply patches to upstream sources "the
right way" or point me to an appropriate document?