Adding More Comments to the Embedded Assets Example (bevyengine#17865)

# Objective

I noticed when I was looking at the embedded assets example that there
wasn't any comments on it to indicate what an embedded asset is and why
anyone would want to make one.

## Solution

I added some more comments to the example that gives more detail about
embedded assets and how they work. Feel free to be aggressive with
rewriting these comments however, I just think the example could use
something haha.

---------

Co-authored-by: Alice Cecile <[email protected]>

Author: Carter0

examples/asset/embedded_asset.rs

@@ -1,5 +1,11 @@
 //! Example of loading an embedded asset.
 
+//! An embedded asset is an asset included in the program's memory, in contrast to other assets that are normally loaded from disk to memory when needed.
+//! The below example embeds the asset at program startup, unlike the common use case of embedding an asset at build time. Embedded an asset at program startup can be useful
+//! for things like loading screens, since it might be nice to display some art while other, non-embedded, assets are loading.
+
+//! One common use case for embedded assets is including them directly within the executable during its creation. By embedding an asset at build time rather than runtime
+//! the program never needs to go to disk for the asset at all, since it is already located in the program's binary executable.
 use bevy::{
     asset::{embedded_asset, io::AssetSourceId, AssetPath},
     prelude::*,