Missing part on diff

Author: twitwi

src/content/lessons/diffusion.mdx

@@ -385,6 +385,12 @@ cal(L)
 </details>
 
 
+## What to fit?
+
+The above derivations reason in terms of fitting the means of the backward steps ~mu_theta (x_t, t)~.
+
+TBD
+
 
 ## Aside: Bayes rule over a Markov chain