Inform on fps_overlay example it requires `bevy_dev_tools` feature

[afonsolage]

How can Bevy's documentation be improved?

Add information on fps_overlay example that the feature bevy_dev_tools is required to use the FpsOverlayPlugin.

This is only relevant if #21236 isn't planned to be merged.

[alice-i-cecile]

We should probably actually just make this a required feature for the example, which will stop users from running the example unless they specify the correct feature.

[mockersf]

it's already a required feature

bevy/Cargo.toml

Lines 4068 to 4072 in eac8bc7

	[[example]]
	name = "fps_overlay"
	path = "examples/dev_tools/fps_overlay.rs"
	doc-scrape-examples = true
	required-features = ["bevy_dev_tools"]

[erictuvesson]

With DevToolsPlugin removed too, is this still relevant?