Write up the "verified" portion of the forward analysis

Signed-off-by: Danila Fedorin <danila.fedorin@gmail.com>

content/blog/04_spa_agda_fixedpoint.md

@@ -55,6 +55,7 @@ Now, let's start with the least element of our lattice, denoted \(\bot\).
 A lattice of finite height is guaranteed to have such an element. If it didn't,
 we could always extend chains by tacking on a smaller element to their bottom,
 and then the lattice wouldn't have a finite height anymore.
+{#start-least}
 
 Now, apply \(f\) to \(\bot\) to get \(f(\bot)\). Since \(\bot\) is the least
 element, it must be true that \(\bot \le f(\bot)\). Now, if it's "less than or equal",