upgrade structures and migrate to nextra v4

content/index.md

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+# Welcome to NoteNextra
+ 
+This was originated from another project [NoteChondria](https://github.com/Trance-0/Notechondria) that I've been working on for a long time but don't have a stable release yet.
+
+I'm not sure if I'll be able to finish it at any time soon. And I've got a lot of materials to share with you guys.
+
+The primary audience of this project is for those challenge takers who are taking courses in Washington University in St. Louis and love Math and Computer Science and want to find something to facilitate their learning.
+
+So here it is. A lite server for you to read my notes.
+
+**Remember, I take notes don't means that I like them and paying attention to the lecture.**
+
+<p style="color: red; font-weight: bold">It's because I'm too easy to fall asleep if I stop doing something on my hand when my mind is wandering.</p>
+
+So I'm not responsible for any wrong notes or facts recorded in my notes since I rarely check them and use them as a reference. I'd like to read the book which have been proof read by many people.
+
+If you find any mistakes, please let me know by submitting an issue in the [GitHub repository](https://github.com/Trance-0/NoteNextra). Or click the `Edit this page` button at the side of the page to fix it yourself with appropriate push request. I really appreciate and willing to accept any valuable contribution in this project.
+
+Enjoy!