Log FPS to console

Use FrameTimeDiagnosticsPlugin to add the information to the diagnostics. Use LogDiagnosticsPlugin to output the diagnostics to the console. You can use bevy::diagnostic::* for some built in diagnostics info to be added.

use bevy::{
    diagnostic::{FrameTimeDiagnosticsPlugin, LogDiagnosticsPlugin},
    prelude::*,
};

fn main() {
    App::new()
        .add_plugins(DefaultPlugins)
        // Adds frame time diagnostics
        .add_plugin(FrameTimeDiagnosticsPlugin::default())
        // Adds a system that prints diagnostics to the console
        .add_plugin(LogDiagnosticsPlugin::default())
        // Any plugin can register diagnostics
        // Uncomment this to add an entity count diagnostics:
        // .add_plugin(bevy::diagnostic::EntityCountDiagnosticsPlugin::default())
        // Uncomment this to add an asset count diagnostics:
        // .add_plugin(bevy::asset::diagnostic::AssetCountDiagnosticsPlugin::<Texture>::default())
        // Uncomment this to add system info diagnostics:
        // .add_plugin(bevy::diagnostic::SystemInformationDiagnosticsPlugin::default())
        .run();
}