format: center repo badges (#6662)

Apply centering proposed at #5983 but not implemented in #6631

Author: davorpa

Diff for: README.md

@@ -1,7 +1,15 @@
 This page is available as an easy-to-read website at [https://ebookfoundation.github.io/](https://ebookfoundation.github.io/free-programming-books/).
 
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 # List of Free Learning Resources In Many Languages
-[![Awesome](https://cdn.rawgit.com/sindresorhus/awesome/d7305f38d29fed78fa85652e3a63e154dd8e8829/media/badge.svg)](https://github.com/sindresorhus/awesome) [![License: CC BY 4.0](https://img.shields.io/badge/License-CC%20BY%204.0-lightgrey.svg)](https://creativecommons.org/licenses/by/4.0/)
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+<div align="center">
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+[![Awesome](https://cdn.rawgit.com/sindresorhus/awesome/d7305f38d29fed78fa85652e3a63e154dd8e8829/media/badge.svg)](https://github.com/sindresorhus/awesome)
+[![License: CC BY 4.0](https://img.shields.io/badge/License-CC%20BY%204.0-lightgrey.svg)](https://creativecommons.org/licenses/by/4.0/)
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+</div>
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 ## Intro