Add last update timestamp to chocolate cake recipe

This seems like a good idea since there have been times where something
new has been discovered (rare but it has happened) or some clarification
has been added (it is, as originally noted, a very complicated recipe).

The date has been backdated to when I last updated it.

2020/ferguson1/chocolate-cake.md

@@ -1,5 +1,7 @@
 # Double-layered Chocolate Fudge Cake
 
+## Last updated Tue 26 Mar 16:28:01 2024 UTC
+
 Here's a delicious double-layered chocolate fudge cake that is
 something of my mum's speciality. It's complicated and I should warn that nobody
 has seemed to get it down as well as she has but it's well worth the effort if
@@ -12,7 +14,7 @@ The picture below was taken for my birthday (14 February) in 2022 as it's the
 best one I have:
 
 <img src="cake.jpg"
- alt="photograth of a delicious double-layered chocolate fudge cake"
+ alt="photograph of a delicious double-layered chocolate fudge cake"
  width=756 height=602>
 
 There are two sets of ingredients and instructions; the cake and the icing. In