Fix creduce example

rustc-grep won't find [E0277] as it's reading it as a regex. The arguments need to be escaped

CONTRIBUTING.md

@@ -490,10 +490,11 @@ to fail to compile `bindgen`'s emitted bindings, you can invoke `predicate.py`
 like this:
 
 ```bash
+# the rustc-grep argument expects a regex, thus escape where necessary
 path/to/rust-bindgen/csmith-fuzzing/predicate.py \
     --bindings-grep NameOfTheStructThatIsErroneouslyDerivingEq \
     --expect-compile-fail \
-    --rustc-grep 'error[E0277]: the trait bound `f64: std::cmp::Eq` is not satisfied' \
+    --rustc-grep 'error\[E0277\]: the trait bound `f64: std::cmp::Eq` is not satisfied' \
     ./isolated-test-case.h
 ```