added known issues

README.md

@@ -21,6 +21,6 @@ cssifier("//a/b[contains(text(), 'hello')]")
 ```
 
 ### Known issues
-[ ] invalid XPath selectors panic
+[ ] invalid XPath return empty String
 
 Contributors are welcome :).

src/lib.rs

@@ -97,5 +97,6 @@ mod tests {
             cssifier("//a/b[contains(text(), 'hello')]").unwrap(),
             "a b:contains(hello)"
         );
+        assert_eq!(cssifier("*random shit//*").unwrap(), "");
     }
 }