Fix accidental removal in visibility grammar.

Author: ehuss

src/visibility-and-privacy.md

@@ -4,6 +4,8 @@
 > _Visibility_ :\
 >       `pub`\
 >    | `pub` `(` `crate` `)`\
+>    | `pub` `(` `self` `)`\
+>    | `pub` `(` `super` `)`\
 >    | `pub` `(` `in` [_SimplePath_] `)`
 
 These two terms are often used interchangeably, and what they are attempting to