Add notice that the functions have been removed from hasbrown

The reasoning seems to be that they do not help LLVM consistently: rust-lang/hashbrown#482

Author: JSorngard

README.md

@@ -17,11 +17,14 @@ if likely(condition) {
 and they should be optimized away by the compiler.
 
 ## Credit
-The functions are taken directly from the [hashbrown](https://crates.io/crates/hashbrown) crate and this crate simply exposes them, all credit belongs to the hashbrown authors.
+The functions are taken directly from the [`hashbrown`](https://crates.io/crates/hashbrown) crate and this crate simply exposes them, all credit belongs to the hashbrown authors.
 
 ## Note
 This is a very minimal crate. If you want more comprehensive functionality, take a look at the [likely_stable](https://crates.io/crates/likely_stable) crate.
 
+`hashbrown`'s implementation of these functions [has been removed](https://github.com/rust-lang/hashbrown/commit/d677fd42df6978522045a9561242588ef970ed0c) with the motivation that they do not help LLVM consistently.
+Verify for yourself with benchmarks if these functions do anything for you.
+
 <br>
 
 ### License