[guide] add link on perf of array iteration methods

Author: ljharb

README.md

@@ -2620,6 +2620,7 @@ Other Style Guides
   - [jQuery Find vs Context, Selector](http://jsperf.com/jquery-find-vs-context-sel/13)
   - [innerHTML vs textContent for script text](http://jsperf.com/innerhtml-vs-textcontent-for-script-text)
   - [Long String Concatenation](http://jsperf.com/ya-string-concat)
+  - [Are Javascript functions like `map()`, `reduce()`, and `filter()` optimized for traversing arrays?](https://www.quora.com/JavaScript-programming-language-Are-Javascript-functions-like-map-reduce-and-filter-already-optimized-for-traversing-array/answer/Quildreen-Motta)
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