Add comment to explain the usage of `font-feature-settings: "ss05"` rule on the DM Mono font

GitOrigin-RevId: f9ec7868a425136a9f4b2b8e8546747dcbf434e3

services/web/frontend/fonts/dm-mono.css

@@ -1,3 +1,9 @@
+/* We're using the "ss05" (stylistic set 5) version of the DM Mono, on the font-feature-settings rule */
+/* https://developer.mozilla.org/en-US/docs/Web/CSS/font-feature-settings */
+/* We use the ss05 specifically to remove the "squiggle" below the f letter. */ 
+/* You can try removing the `font-feature-settings` rule and check what happens to the letter "f", */
+/* as it's quite hard to describe it with sentences alone */
+
 @font-face {
   font-family: 'DM Mono';
   font-feature-settings: 'ss05';