doc: Add example of math

src/content/post/diagram.typ

@@ -1,5 +1,6 @@
 #import "@preview/cetz:0.3.2"
 
+#set text(24pt)
 #metadata((
   title: "Title",
   date: "2025-01-01",
@@ -78,6 +79,10 @@ This is a diagram.
   caption: [Comparison of blog typesetting options]
 )
 
+#html.frame[
+$ lim_(n -> infinity) (1 + 1/n)^n = sum_(n=0)^infinity 1/(n!)
+$]
+
 == Code
 
 #html.frame[```rust