Docs: Info about logging with log ecosystem.

docs/source/logging/logging.md

@@ -1,9 +1,15 @@
 # Logging
 
 The driver uses the [tracing](https://github.com/tokio-rs/tracing) crate for all logs.\
-To view the logs you have to create a `tracing` subscriber to which all logs will be written.
+There are two ways to view the logs:
+- Create a `tracing` subscriber to which all logs will be written (recommended).
+- Enable `log` feature on `tracing` crate and use some logger from `log` ecosystem. \
+Only do this if you can't use `tracing` subscriber for some reason.
+
+## Using tracing subscriber
+
+To print the logs you can use the default subscriber:
 
-To just print the logs you can use the default subscriber:
 ```rust
 # extern crate scylla;
 # extern crate tokio;
@@ -45,4 +51,44 @@ To start this example execute:
 RUST_LOG=info cargo run
 ```
 
-The full [example](https://github.com/scylladb/scylla-rust-driver/tree/main/examples/logging.rs) is available in the `examples` folder
+The full [example](https://github.com/scylladb/scylla-rust-driver/tree/main/examples/logging.rs) is available in the `examples` folder.
+You can run it from main folder of driver repository using `RUST_LOG=trace SCYLLA_URI=<scylla_ip>:9042 cargo run --example logging`.
+
+## Using log
+
+To collect tracing events using log collector you first need to enable `log` feature on `tracing` crate.
+You can use `cargo add tracing -F log` or edit `Cargo.toml`:
+```toml
+tracing = { version = "0.1.40" , features = ["log"] }
+```
+then you can setup `env_logger` os some other logger and it will output logs from the driver:
+
+```rust
+# extern crate scylla;
+# extern crate tokio;
+# extern crate tracing;
+# extern crate env_logger;
+# use std::error::Error;
+# use scylla::{Session, SessionBuilder};
+use tracing::info;
+
+#[tokio::main]
+async fn main() -> Result<(), Box<dyn Error>> {
+    // Setup `log` collector that uses RUST_LOG env variable to configure
+    // verbosity.
+    env_logger::init();
+
+    let uri = std::env::var("SCYLLA_URI").unwrap_or_else(|_| "127.0.0.1:9042".to_string());
+    info!("Connecting to {}", uri);
+
+    let session: Session = SessionBuilder::new().known_node(uri).build().await?;
+    session.query("CREATE KEYSPACE IF NOT EXISTS examples_ks WITH REPLICATION = {'class' : 'NetworkTopologyStrategy', 'replication_factor' : 1}", &[]).await?;
+
+    session.query("USE examples_ks", &[]).await?;
+
+    Ok(())
+}
+```
+
+The full [example](https://github.com/scylladb/scylla-rust-driver/tree/main/examples/logging_log.rs) is available in the `examples` folder.
+You can run it from main folder of driver repository using `RUST_LOG=trace SCYLLA_URI=<scylla_ip>:9042 cargo run --example logging_log`.