Add git content and resources (#3074)

* Update 100-git.md

Added Git introduction and useful links.

* Update content/roadmaps/117-flutter/content/104-version-control-systems/100-git.md

Co-authored-by: Kamran Ahmed <kamranahmed.se@gmail.com>

content/roadmaps/117-flutter/content/104-version-control-systems/100-git.md

@@ -1 +1,10 @@
 # Git
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+[Git](https://git-scm.com/) is a free and open source distributed version control system designed to handle everything from small to very large projects with speed and efficiency.
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+Visit the following resources to learn more:
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+- [Learn Git on the command line](https://github.com/jlord/git-it-electron)
+- [Version Control System Introduction](https://www.youtube.com/watch?v=zbKdDsNNOhg)
+- [Git & GitHub Crash Course For Beginners](https://www.youtube.com/watch?v=SWYqp7iY_Tc)
+- [Learn Git in 20 Minutes](https://youtu.be/Y9XZQO1n_7c?t=21)