update fuzz/README.md to use hex crate

Author: apoelstra

fuzz/README.md

@@ -118,28 +118,12 @@ as follows:
 ```
 #[cfg(test)]
 mod tests {
-    fn extend_vec_from_hex(hex: &str, out: &mut Vec<u8>) {
-        let mut b = 0;
-        for (idx, c) in hex.as_bytes().iter().enumerate() {
-            b <<= 4;
-            match *c {
-                b'A'...b'F' => b |= c - b'A' + 10,
-                b'a'...b'f' => b |= c - b'a' + 10,
-                b'0'...b'9' => b |= c - b'0',
-                _ => panic!("Bad hex"),
-            }
-            if (idx & 1) == 1 {
-                out.push(b);
-                b = 0;
-            }
-        }
-    }
+    use miniscript::bitcoin::hex::FromHex;
 
     #[test]
     fn duplicate_crash() {
-        let mut a = Vec::new();
-        extend_vec_from_hex("048531e80700ae6400670000af5168", &mut a);
-        super::do_test(&a);
+        let v = Vec::from_hex("abcd").unwrap();
+        super::do_test(&v);
     }
 }
 ```