added required changes

- fixed grammar in hint and added more specific link
- added comments in test functions
- changed introduction paragraph

info.toml

@@ -813,8 +813,9 @@ path = "exercises/tests/tests4.rs"
 mode = "test"
 hint = """
 We expect method `Rectangle::new()` to panic for negative values.
-To handle that you need to add special attribute to test function.
-You can refer to the docs: https://doc.rust-lang.org/stable/book/ch11-01-writing-tests.html"""
+To handle that you need to add a special attribute to the test function.
+You can refer to the docs:
+https://doc.rust-lang.org/stable/book/ch11-01-writing-tests.html#checking-for-panics-with-should_panic"""
 
 
 # STANDARD LIBRARY TYPES