Add credit for document icon

Author: BeatLink

README.md

@@ -249,6 +249,7 @@ About
 - The gHacks-User team for allowing the usage of their work
 - All the stargazers (users that are encouraging this project by starring it)
 - Icon was created with images by [OpenClipart-Vectors](https://pixabay.com/users/OpenClipart-Vectors-30363/?utm_source=link-attribution&utm_medium=referral&utm_campaign=image&utm_content=157677) from [Pixabay](https://pixabay.com/?utm_source=link-attribution&utm_medium=referral&utm_campaign=image&utm_content=157677)
+-<div>Icons made by <a href="https://www.flaticon.com/authors/vaadin" title="Vaadin">Vaadin</a> from <a href="https://www.flaticon.com/" 			    title="Flaticon">www.flaticon.com</a> is licensed by <a href="http://creativecommons.org/licenses/by/3.0/" 			    title="Creative Commons BY 3.0" target="_blank">CC 3.0 BY</a></div>
 
 LibreWolf Roadmap
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