Update README to clarify contribution conditions

Previously this was talking about contributions to Serde rather than jobserver-rs.

Author: zeramorphic

README.md

@@ -35,5 +35,5 @@ at your option.
 ### Contribution
 
 Unless you explicitly state otherwise, any contribution intentionally submitted
-for inclusion in Serde by you, as defined in the Apache-2.0 license, shall be
+for inclusion in jobserver-rs by you, as defined in the Apache-2.0 license, shall be
 dual licensed as above, without any additional terms or conditions.