add section 15.5 - Ternaries

add link to the relevant eslint rule

Author: bgits

README.md

@@ -1289,6 +1289,29 @@ Other Style Guides
 
   - [15.4](#15.4) <a name='15.4'></a> For more information see [Truth Equality and JavaScript](http://javascriptweblog.wordpress.com/2011/02/07/truth-equality-and-javascript/#more-2108) by Angus Croll.
 
+  - [15.5](#15.5) <a name='15.5'></a> Ternaries should not be nested and generally be single line expressions.
+ 
+    eslint rules: [`no-nested-ternary`](http://eslint.org/docs/rules/no-nested-ternary.html).
+    
+    ```javascript
+    //bad
+    const foo = maybe1 > maybe2
+      ? "bar"
+      : value1 > value2 ? "baz" : null;
+     
+    //better
+    const maybeNull = value1 > value2 ? 'baz' : null;
+    
+    const foo = maybe1 > maybe2
+      ? 'bar'
+      : maybeNull;
+    
+    //best
+    const maybeNull = value1 > value2 ? 'baz' : null;
+    
+    const foo = maybe1 > maybe2 ? 'bar' : maybeNull;
+    ```
+    
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