Rollup merge of rust-lang#73720 - GuillaumeGomez:cleanup-e0704, r=Dylan-DPC

Clean up E0704 error explanation

r? @Dylan-DPC

Author: Manishearth

src/librustc_error_codes/error_codes/E0704.md

@@ -1,6 +1,6 @@
-This error indicates that a incorrect visibility restriction was specified.
+An incorrect visibility restriction was specified.
 
-Example of erroneous code:
+Erroneous code example:
 
 ```compile_fail,E0704
 mod foo {
@@ -12,6 +12,7 @@ mod foo {
 
 To make struct `Bar` only visible in module `foo` the `in` keyword should be
 used:
+
 ```
 mod foo {
     pub(in crate::foo) struct Bar {