Add lean course (#671)

Tried to follow the instructions to add course. If there are any issues
feel free to adjust, or tell me so I can fix it.

Author: nimarasekh

data/courses.yaml

@@ -17,6 +17,16 @@
 # a general subject (`mathematics`, `logic`, `computer science`).
 #
 # This list is not ordered. Add new entries wherever you want.
+- name: "Mathematical Proofs with Computers"
+  instructor: Nima Rasekh
+  institution: University of Greifswald
+  lean_version: 4
+  tags: ['mathematics', 'beginner']
+  summary: >
+    This is a bachelor's level course introducing the basics of formalization via Lean (definitions, tactics, structures), as well as some of the libraries in Mathlib (set theory, number theory, algebra), following the structure of the book 'Mathematics in Lean'. The course culminated in a student project, where the students pursued a formalization project based on their individual interests.
+  website: https://github.com/nimarasekh/Formalization-SoSe25/
+  material: https://leanprover-community.github.io/mathematics_in_lean/
+  year: 2025
 - name: "Formal Methods in Mathematics"
   instructor: Johan Commelin (UU) and Sander Dahmen (VU)
   institution: Mastermath (Dutch universities collaboration)