set RFC number

Author: RalfJung

text/0000-float-semantics.md renamed to text/3514-float-semantics.md

@@ -1,6 +1,6 @@
 - Feature Name: `float_semantics`
 - Start Date: 2023-10-14
-- RFC PR: [rust-lang/rfcs#0000](https://github.com/rust-lang/rfcs/pull/0000)
+- RFC PR: [rust-lang/rfcs#3514](https://github.com/rust-lang/rfcs/pull/3514)
 - Rust Issue: [rust-lang/rust#0000](https://github.com/rust-lang/rust/issues/0000)
 
 # Summary