update example docs

Author: teh-cmc

examples/rust/stdio/src/main.rs

@@ -1,5 +1,10 @@
 //! Demonstrates how to log data to standard output with the Rerun SDK, and then visualize it
 //! from standard input with the Rerun Viewer.
+//!
+//! Usage:
+//! ```text
+//! echo 'hello from stdin!' | cargo run | rerun -
+//! ```
 
 fn main() -> Result<(), Box<dyn std::error::Error>> {
     let rec = rerun::RecordingStreamBuilder::new("rerun_example_stdio").stdout()?;