Update ToastAndroid with changes in Android 11 (facebook#4213)

Author: pafry7

docs/toastandroid.md

@@ -12,6 +12,8 @@ You can alternatively use `showWithGravity(message, duration, gravity)` to speci
 
 The `showWithGravityAndOffset(message, duration, gravity, xOffset, yOffset)` method adds the ability to specify an offset with in pixels.
 
+> Starting with Android 11 (API level 30), setting the gravity has no effect on text toasts. Read about the changes [here](https://developer.android.com/about/versions/11/behavior-changes-11#text-toast-api-changes).
+
 ```SnackPlayer name=Toast%20Android%20API%20Example&supportedPlatforms=android
 import React from 'react';
 import {StyleSheet, ToastAndroid, Button, StatusBar} from 'react-native';
@@ -86,6 +88,8 @@ static show(message: string, duration: number);
 
 ### `showWithGravity()`
 
+This property will only work on Android API 29 and below. For similar functionality on higher Android APIs, consider using snackbar or notification.
+
 ```tsx
 static showWithGravity(message: string, duration: number, gravity: number);
 ```
@@ -94,6 +98,8 @@ static showWithGravity(message: string, duration: number, gravity: number);
 
 ### `showWithGravityAndOffset()`
 
+This property will only work on Android API 29 and below. For similar functionality on higher Android APIs, consider using snackbar or notification.
+
 ```tsx
 static showWithGravityAndOffset(
   message: string,