docs: Include tracing example

Cargo.toml

@@ -33,3 +33,6 @@ clap = { version = "3.0", default-features = false, features = ["std", "derive"]
 
 [dev-dependencies]
 env_logger = "0.9.0"
+tracing = "0.1"
+tracing-subscriber = "0.2"
+tracing-log = "0.1.3"

examples/example.rs

@@ -14,4 +14,10 @@ fn main() {
     env_logger::Builder::new()
         .filter_level(cli.verbose.log_level_filter())
         .init();
+
+    log::error!("Engines exploded");
+    log::warn!("Engines smoking");
+    log::info!("Engines exist");
+    log::debug!("Engine temperature is 200 degrees");
+    log::trace!("Engine subsection is 300 degrees");
 }

examples/example_tracing.rs

@@ -0,0 +1,34 @@
+use clap::Parser;
+use clap_verbosity_flag::Verbosity;
+
+/// Foo
+#[derive(Debug, Parser)]
+struct Cli {
+    #[clap(flatten)]
+    verbose: Verbosity,
+}
+
+fn main() {
+    let cli = Cli::parse();
+
+    tracing_subscriber::fmt()
+        .with_max_level(convert_filter(cli.verbose.log_level_filter()))
+        .init();
+
+    log::error!("Engines exploded");
+    log::warn!("Engines smoking");
+    log::info!("Engines exist");
+    log::debug!("Engine temperature is 200 degrees");
+    log::trace!("Engine subsection is 300 degrees");
+}
+
+fn convert_filter(filter: log::LevelFilter) -> tracing_subscriber::filter::LevelFilter {
+    match filter {
+        log::LevelFilter::Off => tracing_subscriber::filter::LevelFilter::OFF,
+        log::LevelFilter::Error => tracing_subscriber::filter::LevelFilter::ERROR,
+        log::LevelFilter::Warn => tracing_subscriber::filter::LevelFilter::WARN,
+        log::LevelFilter::Info => tracing_subscriber::filter::LevelFilter::INFO,
+        log::LevelFilter::Debug => tracing_subscriber::filter::LevelFilter::DEBUG,
+        log::LevelFilter::Trace => tracing_subscriber::filter::LevelFilter::TRACE,
+    }
+}