Remove 'arrow keys' from history-substring-search description

modules/history-substring-search/README.md

@@ -3,8 +3,8 @@ History Substring Search
 
 Integrates [zsh-history-substring-search][1] into Oh My Zsh, which implements
 the [Fish shell][2]'s history search feature, where the user can type in any
-part of a previously entered command and press the `UP` and `DOWN` arrow keys
-to cycle through matching commands.
+part of a previously entered command and press up and down to cycle through
+matching commands.
 
 If this module is used in conjuncture with the *syntax-highlighting* module, it
 must be loaded **after** it.