extend on-unimplemented docs

Author: estebank

src/doc/unstable-book/src/language-features/on-unimplemented.md

@@ -139,7 +139,8 @@ error[E0277]: `&str` is not an iterator
   = note: required by `std::iter::IntoIterator::into_iter`
 ```
 
-If you need to filter on multiple attributes, you can use `all` in the following way:
+If you need to filter on multiple attributes, you can use `all`, `any` or
+`not` in the following way:
 
 ```rust,compile_fail
 #[rustc_on_unimplemented(
@@ -149,4 +150,4 @@ If you need to filter on multiple attributes, you can use `all` in the following
     )
 )]
 pub trait From<T>: Sized { /* ... */ }
-```
+```