Fix some typos in NativeModulesAndroid.md

Summary:
Hi, here are some typo fixes in the documentation related to Android native modules:
* Add missing package and imports for the second part of the basic tutorial (register module)
* Add missing `public` keyword
* Remove incongruous word
Closes https://github.com/facebook/react-native/pull/11938

Differential Revision: D4439220

Pulled By: hramos

fbshipit-source-id: e7086fe384ed6238306abf0ee72c944fac53ad7b

docs/NativeModulesAndroid.md

@@ -98,7 +98,19 @@ Read more about [ReadableMap](https://github.com/facebook/react-native/blob/mast
 The last step within Java is to register the Module; this happens in the `createNativeModules` of your apps package. If a module is not registered it will not be available from JavaScript.
 
 ```java
-class AnExampleReactPackage implements ReactPackage {
+package com.facebook.react.modules.toast;
+
+import com.facebook.react.ReactPackage;
+import com.facebook.react.bridge.JavaScriptModule;
+import com.facebook.react.bridge.NativeModule;
+import com.facebook.react.bridge.ReactApplicationContext;
+import com.facebook.react.uimanager.ViewManager;
+
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
+
+public class AnExampleReactPackage implements ReactPackage {
 
   @Override
   public List<Class<? extends JavaScriptModule>> createJSModules() {
@@ -326,7 +338,7 @@ componentWillMount: function() {
 
 ### Getting activity result from `startActivityForResult`
 
-You'll need to listen to `onActivityResult` if you want to get results from an activity you started with `startActivityForResult`. To do this, the you must extend `BaseActivityEventListener` or implement `ActivityEventListener`. The former is preferred as it is more resilient to API changes. Then, you need to register the listener in the module's constructor,
+You'll need to listen to `onActivityResult` if you want to get results from an activity you started with `startActivityForResult`. To do this, you must extend `BaseActivityEventListener` or implement `ActivityEventListener`. The former is preferred as it is more resilient to API changes. Then, you need to register the listener in the module's constructor,
 
 ```java
 reactContext.addActivityEventListener(mActivityResultListener);