Update README.md

Author: mahmoudmaray2000

README.md

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 ![Flutter](https://user-images.githubusercontent.com/73144855/127227640-07449388-be61-4675-88c7-86dc1058cbef.jpg)
 
-**What is Flutter**
+##**What is Flutter**
 
 Flutter is a free and open-source mobile UI framework created by Google and released in May 2017. In a few words, it allows you to create a native mobile application with only one codebase. This means that you can use one programming language and one codebase to create two different apps (for iOS and Android).
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