Fix header hierarchy

Co-authored-by: Eric Huss <[email protected]>

Author: danielhenrymantilla

src/macros-by-example.md

@@ -76,7 +76,7 @@ delimiters for the matcher will match any pair of delimiters. Thus, for
 instance, the matcher `(())` will match `{()}` but not `{{}}`. The character
 `$` cannot be matched or transcribed literally.
 
-#### Forwarding a matched fragment
+### Forwarding a matched fragment
 
 When forwarding a matched fragment to another macro-by-example, matchers in
 the second macro will see an opaque AST of the fragment type. The second macro