Update README

README.md

@@ -5,13 +5,18 @@
 
 display expression using `{:#x?}` format when false assertion causes `panic!()`.
 
-# why
+# Why
 Writing and testing protocol level libraries requires many tests to be written
 with respect to byte level protocol sections in hex. This library simplifies the process
 of viewing the differences between these types when tests fail by displaying by using the
 `{:#x?}` representation.
 
-# usage
+# Usage
+*Compiler support: requires rustc 1.39+*
+```
+$ cargo add assert_hex
+```
+
 Replace `assert_eq` or `assert_ne` with `assert_eq_hex` or `assert_ne_hex`
 respectively.