Update native-modules-android.md

Summary:
`import com.facebook.react.bridge.Callback;` is needed to be able to use `Callback` as a parameter.

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Thought it needed to be clearer that you need to import `Callback` as it's not a native Java type.

(Write your test plan here. If you changed any code, please provide us with clear instructions on how you verified your changes work. Bonus points for screenshots and videos!)

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  CATEGORY
[----------]        TYPE
[ CLI      ]   [-------------]      LOCATION
[ DOCS     ]   [ BREAKING    ]   [-------------]
[ GENERAL  ]   [ BUGFIX      ]   [-{Component}-]
[ INTERNAL ]   [ ENHANCEMENT ]   [ {File}      ]
[ IOS      ]   [ FEATURE     ]   [ {Directory} ]   |-----------|
[ ANDROID  ]   [ MINOR       ]   [ {Framework} ] - | {Message} |
[----------]   [-------------]   [-------------]   |-----------|

[CATEGORY] [TYPE] [LOCATION] - MESSAGE

 EXAMPLES:

 [IOS] [BREAKING] [FlatList] - Change a thing that breaks other things
 [ANDROID] [BUGFIX] [TextInput] - Did a thing to TextInput
 [CLI] [FEATURE] [local-cli/info/info.js] - CLI easier to do things with
 [DOCS] [BUGFIX] [GettingStarted.md] - Accidentally a thing/word
 [GENERAL] [ENHANCEMENT] [Yoga] - Added new yoga thing/position
 [INTERNAL] [FEATURE] [./scripts] - Added thing to script that nobody will see
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Closes #17015

Differential Revision: D6464454

Pulled By: hramos

fbshipit-source-id: dfb57f4176483c4e95539c5db03a86f01892e587

docs/native-modules-android.md

@@ -171,6 +171,8 @@ ToastExample.show('Awesome', ToastExample.SHORT);
 Native modules also support a special kind of argument - a callback. In most cases it is used to provide the function call result to JavaScript.
 
 ```java
+import com.facebook.react.bridge.Callback;
+
 public class UIManagerModule extends ReactContextBaseJavaModule {
 
 ...