Update textbook.en.md

12.temporary_ins/05.coordinates-systems/30.cylindrical-coordinates/10.main/textbook.en.md

@@ -8,6 +8,8 @@ lessons:
       order:
     - slug: cylindrical-coordinates-linear
       order: 1
+    - slug: es-en-cylindrical-coordinates-exchange
+      order: 3
 ---
 <!--caligraphie de l'intégrale double curviligne-->
 $`\def\oiint{\displaystyle\mathop{{\iint}\mkern-18mu \scriptsize \bigcirc}}`$