Refactor: Categorize tips in tips.json and build GitBook structure

Author: hemanth

docs/README.md

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+# Git Tips
+
+Welcome to the Git Tips documentation! Browse through the categories in the sidebar to find useful Git commands and tricks.

docs/SUMMARY.md

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+# Summary
+
+* [Introduction](README.md)
+* [Basic Operations](basic-operations.md)
+* [Branching](branching.md)
+* [Log and History](log-and-history.md)
+* [Merging and Rebasing](merging-and-rebasing.md)
+* [Miscellaneous](miscellaneous.md)
+* [Remotes](remotes.md)
+* [Setup and Config](setup-and-config.md)
+* [Stashing](stashing.md)
+* [Submodules and Subtrees](submodules-and-subtrees.md)
+* [Tagging](tagging.md)
+* [Undoing Changes](undoing-changes.md)