Fix formatting of irradiance_volumes example instructions (#15842)

# Objective

Fix minor text formatting issue introduced in #15033

Before:

<img width="1280" alt="image"
src="https://github.com/user-attachments/assets/cec4302b-a7cf-4afb-82f8-7354fa5fea00">

After:

<img width="1280" alt="image"
src="https://github.com/user-attachments/assets/ab62e58b-e563-4250-842f-90bed3a153a1">

## Solution

Add explicit linebreaks and `\` to ignore indentation on following
lines.

## Testing

`cargo run --example irradiance_volumes`

examples/3d/irradiance_volumes.rs

@@ -341,11 +341,11 @@ impl AppStatus {
  };
 
  format!(
- "{CLICK_TO_MOVE_HELP_TEXT}
- {voxels_help_text}
- {irradiance_volume_help_text}
- {rotation_help_text}
- {switch_mesh_help_text}"
+ "{CLICK_TO_MOVE_HELP_TEXT}\n\
+  {voxels_help_text}\n\
+  {irradiance_volume_help_text}\n\
+  {rotation_help_text}\n\
+  {switch_mesh_help_text}"
  )
  .into()
  }