docs: mention icons on training homepage

Author: james

docs/language/learn-ql/ql-training.rst

@@ -19,7 +19,10 @@ Start learning how to use QL in variant analysis for a specific language by look
 
 .. |arrow-r| unicode:: U+2192
 
-When you have selected a presentation, use |arrow-r| and |arrow-l| to navigate between slides, press **p** to view the additional notes for a slide (where available), and press **f** to enter full-screen mode.
+.. |info| unicode:: U+24D8
+
+When you have selected a presentation, use |arrow-r| and |arrow-l| to navigate between slides.
+Press **p** to view the additional notes on slides that have an information icon |info| in the top right corner, and press **f** to enter full-screen mode.
 
 The presentations contain a number of QL query examples.
 We recommend that you download `QL for Eclipse <https://help.semmle.com/ql-for-eclipse/Content/WebHelp/home-page.html>`__ and import the example snapshot for each presentation so that you can find the bugs mentioned in the slides.