Convert links to markdown format

preface.md

@@ -0,0 +1,35 @@
+**Preface**
+
+This exists because we believe learning math should be enjoyable for everyone. These notes are meant as a reference for anyone studying the same topics and wanting a cross-reference.
+
+Since doing this alone, we couldn't cross-reference with anyone else. So this preface is an invitation: create and publish your own notes. If you can't create or publish solo, maybe we can start a math club — a more laid-back format to share things.
+
+**Resources**
+
+**Getting Started**
+- [OSSU Math](https://github.com/ossu/math) (free curriculum)
+- [Math Major Guide: Nonstandard Advice](https://www.youtube.com/watch?v=EE7KpcReYw4)
+- [Learn Mathematics from START to FINISH](https://www.youtube.com/watch?v=pTnEG_WGd2Q)
+
+**Lectures & Courses**
+- [Khan Academy](https://www.khanacademy.org/)
+- [MIT OpenCourseWare: Linear Algebra](https://ocw.mit.edu/courses/18-06sc-linear-algebra-fall-2011/)
+- [Start Learning Mathematics (playlist)](https://www.youtube.com/playlist?list=PLBh2i93oe2qtbygdXz4u6Mkh7c_hMLBA8)
+
+**Books & Textbooks**
+- [Openstax](https://openstax.org/subjects/math) (free textbooks)
+- [AIM Open Textbook](https://textbooks.aimath.org/) (free)
+
+**Videos (Motivation & Insight)**
+- [NancyPi](https://www.youtube.com/@NancyPi/featured)
+- [Eddie Woo](https://www.youtube.com/@misterwootube/featured)
+- [Mathologer](https://www.youtube.com/@Mathologer/featured)
+- [The Math Sorcerer](https://www.youtube.com/@TheMathSorcerer/featured)
+- [Numberphile](https://www.youtube.com/@numberphile/featured)
+- [The Bright Side of Mathematics](https://www.youtube.com/@brightsideofmaths/videos)
+- [Daniel Rubin](https://www.youtube.com/@DanielRubin1/featured)
+- [Professor Leonard](https://www.youtube.com/@ProfessorLeonard/featured)
+
+**Tools (Practice & Visualization)**
+- [Wolfram Alpha](https://www.wolframalpha.com/)
+- [GeoGebra Calculator Suite](https://www.geogebra.org/calculator)