Create FUNDING.yml

As discussed on Zulip, we'd like to give it a try.

Author: phip1611

.github/FUNDING.yml

@@ -0,0 +1,4 @@
+# If you are a frequent contributor to uefi-rs and would like to be featured in
+# the sponsors section, please contact the maintainers.
+
+github: phip1611