[prompt] Remove spurious duplicate section

Remove duplication 'Prompt Display Length' section.
Also, adjust wrapping for `~`.

modules/prompt/README.md

@@ -19,21 +19,13 @@ zstyle ':prezto:module:prompt' theme 'name'
 ### Prompt Display Length
 
 To change working directory prompt display length from 'short', set the
-following to 'long' (without '~' expansion) or 'full' (with '~' expansion)
+following to 'long' (without `~` expansion) or 'full' (with `~` expansion)
 in *zpreztorc*.
 
 ```sh
 zstyle ':prezto:module:prompt' pwd-length 'short'
 ```
 
-### Prompt Display Length
-
-To change working directory prompt display length from 'short', set the
-following to 'long' (without '~' expansion) or 'full' (with '~' expansion)
-in *zpreztorc*.
-
-    zstyle ':prezto:module:prompt' pwd-length 'short'
-
 Theming
 -------