add example of custom title for alert syntax

Author: vburzynski

_template/how-to/alerts-admonitions-callouts.md

@@ -38,8 +38,17 @@
 > }
 > ```
 
+### Callout With Custom Title
+
+> [!IMPORTANT] Pay Attention!
+> Crucial information necessary for users to succeed.
+
+## Syntax Incompatible With GitHub
+
 ### Nested Alerts
 
+While Obsidian supports rendering nested callouts, at the time of writing GitHub does not:
+
 > [!NOTE]  
 > Highlights information that users should take into account, even when skimming.
 > > [!TIP]