Add css grid todo refactor note

Looking at it, we could really use a good refactor to use the CSS
grid for the main page layout. Some considerations though:

 - The sidebar
 - The printable page view

...we'll need to make sure we account for all these things when
refactoring.

themes/default/theme.css

@@ -50,6 +50,8 @@
 	/* #ffdb6d #36962c hsl(36, 78%, 80%) hsla(262, 92%, 68%, 0.42) */
 }
 
+/* TODO: Refactor to use the CSS grid */
+
 body { margin: 2rem 0 0 0; background: var(--bg-back); line-height: 1.45em; color: var(--text-dark); font-family: sans-serif; }
 
 nav { display: flex; background-color: var(--accent-a2); color: var(--accent-b1);  }