Adding explanation for loading additonal audio formats to example (be…

…vyengine#12998)

# Objective

Fixes bevyengine#12900

## Solution

Added comment to example indicating that additional audio formats are
supported when the feature is added.

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Co-authored-by: James Liu <[email protected]>

examples/audio/audio.rs

@@ -1,4 +1,5 @@
 //! This example illustrates how to load and play an audio file.
+//! For loading additional audio formats, you can enable the corresponding feature for that audio format.
 
 use bevy::prelude::*;