Add license text for py-sdl2 Public Domain license

Package is currently under review [1]. Fedora Legal approved this as a Public Domain license [2].

[1] https://bugzilla.redhat.com/show_bug.cgi?id=2283541 [2] https://lists.fedoraproject.org/archives/list/legal@lists.fedoraproject.org/message/44KT5NKIT77ZWME464KDBYNH6WBCG4DA/