Update cheatsheet.fr.md

00.brainstorming-pedagogical-teams/40.collection-existing-pedagogical-content/42.relativistic-mechanics/20.n2/20.overview/cheatsheet.fr.md

@@ -8,6 +8,13 @@ lessons:
       order: 1
     - slug: relativity-linear-2
       order: 2
+    - slug: relativity-123-overview-panorama
+      order: 2
+    - slug: relativity-234-overview-panorama
+      order: 1
+---
+
+Les relativités niveau 2 : main
 ---
 
 #### Mécaniques relativistes, n2, synthèse