Add syntax highlighting to docs where missing

docs/apis/AppRegistry.md

@@ -51,7 +51,7 @@ into `runApplication`
 
 ## Example
 
-```
+```js
 AppRegistry.registerComponent('MyApp', () => AppComponent)
 AppRegistry.runApplication('MyApp', {
   initialProps: {},

docs/apis/NetInfo.md

@@ -44,7 +44,7 @@ internet connectivity.
 
 Fetching the connection type:
 
-```
+```js
 NetInfo.fetch().then((connectionType) => {
   console.log('Connection type:', connectionType);
 });