Better panic message.

src/prob2/mod.rs

@@ -40,7 +40,10 @@ impl From<char> for Play {
             'X' => Play::Rock,
             'Y' => Play::Paper,
             'Z' => Play::Scissors,
-            _ => panic!("Only A, B, C, X, Y or Z letters are available."),
+            other => panic!(
+                "Only A, B, C, X, Y or Z letters are available. Had {}",
+                other
+            ),
         }
     }
 }