Update cheatsheet.fr.md

00.brainstorming-pedagogical-teams/40.collection-existing-pedagogical-content/05.classical-mechanics/vector-analysis/cheatsheet.fr.md

@@ -121,6 +121,14 @@ can vary the coordinates and see the displacement of the point M.
 
 ![](mechanics-vectors-collinear.png)
 
+#### Base vectorial / Base vectorielle / Base of a vector space
+
+En un plano $`\mathcal{P}`$ / Dans un plan $`\mathcal{P}`$ / In a plane $`\mathcal{P}`$
+
+*[ReadyForUse]*
+
+![](mechanics-vector-base-plane_L1200.gif)
+