Update book regarding wait_indefinitely (google#201)

book/src/applet/prelude/button.md

@@ -51,10 +51,10 @@ to leak it. This is equivalent to calling `core::mem::forget()`.
 {{#include button1.rs:leak}}
 ```
 
-Finally, we just endlessly wait for callbacks. This step will eventually not be
-needed. Waiting for callbacks indefinitely will be the implicit behavior when
-`main` exits, in which case `main` can be seen as a callback setup procedure.
-The `scheduling::wait_for_callback()` function puts the applet to sleep until a
+Finally, we just endlessly wait for callbacks. This step is optional: waiting
+for callbacks indefinitely is the implicit behavior when `main` exits. In some
+way, `main` can be seen as a callback setup procedure. The
+`scheduling::wait_for_callback()` function puts the applet to sleep until a
 callback is scheduled and `scheduled::wait_indefinitely()` is just an infinite
 loop around `wait_for_callback()`.
 

book/src/applet/prelude/button2.rs

@@ -68,8 +68,5 @@ fn main() {
         button::Listener::new(button_index, handler).leak();
         //} ANCHOR_END: listener
     }
-
-    // We indefinitely wait for callbacks.
-    scheduling::wait_indefinitely();
 }
 //} ANCHOR_END: all

crates/prelude/CHANGELOG.md

@@ -12,6 +12,7 @@
 
 ### Patch
 
+- Update documentation
 - Fix clippy lints
 - Update dependencies
 

crates/prelude/src/scheduling.rs

@@ -41,6 +41,8 @@ pub fn wait_until(mut cond: impl FnMut() -> bool) {
 }
 
 /// Waits for callbacks indefinitely.
+///
+/// This is the default behavior when returning from `main()`.
 pub fn wait_indefinitely() -> ! {
     loop {
         wait_for_callback();

examples/rust/led/src/lib.rs

@@ -55,7 +55,4 @@ fn main() {
         // We indefinitely listen by creating and leaking a listener.
         button::Listener::new(button_index, handler).leak();
     }
-
-    // We indefinitely wait for callbacks.
-    scheduling::wait_indefinitely();
 }