Add an example of <details> block usage.

Note the markdown=1 attribute.

test/default.md

@@ -33,6 +33,24 @@ circle constant $\tau$
   dandelion okra wakame tomato. Dandelion cucumber earthnut pea peanut soko zucchini. 
   
 
+<!-- Expandable sections -->
+
+<details markdown=1>
+
+<summary>
+    VOIR LA SOLUTION
+</summary>
+
+```math
+f\colon\left\{\begin{aligned}\mathbb{R}_4[X]&\longrightarrow\mathbb{R}_4[X] \\
+P&\longmapsto P’\end{aligned}\right.
+\qquad
+g\colon\left\{\begin{aligned}\mathbb{R}_2[X]&\longrightarrow\mathbb{R}_2[X] \\
+P&\longmapsto XP’+P\end{aligned}\right.
+```
+
+</details>
+
 
 <!-- Trailing # are ignored and are sometimes good for readability -->
 ### Flowchart ########################################################
@@ -54,10 +72,12 @@ graph LR
   Pipeline --> |updates| Website
 ```
 
-#### Imagine 💾🐘🐘🐘🐘🐢
+
+
+### LateX 💾🐘🐘🐘🐘🐢
 
 ```math
-e^{i\tau}=1
+f\colon\left\{\begin{aligned}\mathbb{R}_4[X]&\longrightarrow\mathbb{R}_4[X] \\P&\longmapsto P’\end{aligned}\right. \qquad g\colon\left\{\begin{aligned}\mathbb{R}_2[X]&\longrightarrow\mathbb{R}_2[X] \\ P&\longmapsto XP’+P\end{aligned}\right.
 ```
 
 > The complex exponential of the circle constant is unity.