Keyboard will show documentation

Summary:
Clarified documentation for keyboardWillShow on Android as seen in issue #14275

Clarifies documentation of keyboardWillShow

None as it is just a comment that changed.
Closes #14350

Differential Revision: D5275173

Pulled By: shergin

fbshipit-source-id: d4fb08de71e6be40bb363dfc82d38b191570c476

Libraries/Components/Keyboard/Keyboard.js

@@ -100,7 +100,9 @@ let Keyboard = {
  * - `keyboardDidChangeFrame`
  *
  * Note that if you set `android:windowSoftInputMode` to `adjustResize` or `adjustNothing`,
- * only `keyboardDidShow` and `keyboardDidHide` events will available on Android.
+ * only `keyboardDidShow` and `keyboardDidHide` events will be available on Android.
+ * `keyboardWillShow` as well as `keyboardWillHide` are generally not available on Android
+ * since there is no native corresponding event.
  *
  * @param {function} callback function to be called when the event fires.
  */