add react hooks section

AWolf81 · Rokt33r · commit 1601292db73a · 2019-05-13T14:05:57.000+09:00
diff --git a/docs/code_style.md b/docs/code_style.md
@@ -79,4 +79,11 @@ class MyComponent extends React.Component {
     // code goes here...
   }
 }
-```
+```
+
+## React Hooks
+Existing code will be kept class-based and will only be changed to functional components with hooks if it improves readability or makes things more reusable. 
+
+For new components it's OK to use hooks with functional components but don't mix hooks & class-based components within a feature - just for code style / readability reasons. 
+
+Read more about hooks in the [React hooks introduction](https://reactjs.org/docs/hooks-intro.html).

Original file line number	Diff line number	Diff line change
`@@ -79,4 +79,11 @@ class MyComponent extends React.Component {`
`79`	`79`	`// code goes here...`
`80`	`80`	`}`
`81`	`81`	`}`
`82`		-```
	`82`	+```
	`83`	`+`
	`84`	`+## React Hooks`
	`85`	`+Existing code will be kept class-based and will only be changed to functional components with hooks if it improves readability or makes things more reusable.`
	`86`	`+`
	`87`	`+For new components it's OK to use hooks with functional components but don't mix hooks & class-based components within a feature - just for code style / readability reasons.`
	`88`	`+`
	`89`	`+Read more about hooks in the [React hooks introduction](https://reactjs.org/docs/hooks-intro.html).`