README: Fix FAQ entry about isearch highlighting

Fixes zsh-users#423

Author: m0vie

README.md

@@ -47,17 +47,18 @@ syntax highlighting.
 ### Does syntax highlighting work during incremental history search?
 
 Highlighting the command line during an incremental history search (by default bound to
-to <kbd>Ctrl+R</kbd> in zsh's emacs keymap) requires zsh 5.3.2 or newer.
+to <kbd>Ctrl+R</kbd> in zsh's emacs keymap) requires zsh 5.4 or newer.
 
-Under zsh 5.3.1 and older, the zsh-default [underlining][zshzle-Character-Highlighting]
+Under version older than 5.4, the zsh-default [underlining][zshzle-Character-Highlighting]
 of the matched portion of the buffer remains available, but zsh-syntax-highlighting's
 additional highlighting is unavailable.  (Those versions of zsh do not provide
 enough information to allow computing the highlighting correctly.)
 
-See [issue #288][i288] for details.
+See issues [#288][i288] and [#415][i415] for details.
 
 [zshzle-Character-Highlighting]: http://zsh.sourceforge.net/Doc/Release/Zsh-Line-Editor.html#Character-Highlighting
 [i288]: https://github.com/zsh-users/zsh-syntax-highlighting/pull/288
+[i415]: https://github.com/zsh-users/zsh-syntax-highlighting/pull/415
 
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