Update timers-and-reminders.md

Author: joproulx

docs/orleans/grains/timers-and-reminders.md

@@ -6,6 +6,10 @@ ms.date: 08/01/2024
 
 # Timers and reminders
 
+The Orleans runtime provides two mechanisms, called timers and reminders, that enable the developer to specify periodic behavior for grains.
+
+## Timers
+
 **Timers** are used to create periodic grain behavior that isn't required to span multiple activations (instantiations of the grain). A timer is identical to the standard .NET <xref:System.Threading.Timer?displayProperty=fullName> class. In addition, timers are subject to single-threaded execution guarantees within the grain activation that they operate on.
 
 Each activation may have zero or more timers associated with it. The runtime executes each timer routine within the runtime context of the activation that it's associated with.