Docs: By-example App priorities and message passing
# Message passing & capacity
-Software tasks have support for message passing, this means that they can be spawned with an argument
-as `foo::spawn(1)` which will run the task `foo` with the argument `1`. The number of arguments is not
-limited and is exemplified in the following:
+Software tasks support message passing, this means that software tasks can be spawned
+with an argument: `foo::spawn(1)` which will run the task `foo` with the argument `1`.
+
+Capacity sets the size of the spawn queue for the task, if not specified capacity defaults to 1.
+
+In the example below, the capacity of task `foo` is `3`, allowing three simultaneous
+pending spawns of `foo`. Exceeding this capacity is an `Error`.
+
+The number of arguments to a task is not limited:
``` rust
{{#include ../../../../examples/message_passing.rs}}
