add unimplemented tip when binary feature is disabled

bingus/src/lib.rs

@@ -222,7 +222,7 @@ mod dynamic {
                             buf
                         }),
                         #[cfg(not(feature = "binary"))]
-                        _ => unimplemented!("no format available to open this thing"),
+                        _ => unimplemented!("no format reader available to open this thing (turn on the 'binary' feature to default to binary data)"),
                     })
                 },
             )