docs: add comment to PING_TIMER

Author: JosephGoulden

lightning-background-processor/src/lib.rs

@@ -52,6 +52,8 @@ const FRESHNESS_TIMER: u64 = 1;
 
 #[cfg(not(debug_assertions))]
 const PING_TIMER: u64 = 5;
+/// Signature operations take a lot longer without compiler optimisations.
+/// Increasing the ping timer allows for this but slower devices will be disconnected if the timeout is reached.
 #[cfg(debug_assertions)]
 const PING_TIMER: u64 = 30;