Update `rtt/src/lib.rs` test
//! // Read from a channel
//! if let Some(input) = rtt.up_channels().take(0) {
//! let mut buf = [0u8; 1024];
-//! let count = input.read(&mut buf[..])?;
+//! let count = input.read(&mut core, &mut buf[..])?;
//!
//! println!("Read data: {:?}", &buf[..count]);
//! }
//!
//! // Write to a channel
//! if let Some(output) = rtt.down_channels().take(0) {
-//! output.write(b"Hello, computer!\n")?;
+//! output.write(&mut core, b"Hello, computer!\n")?;
//! }
//!
//! # Ok::<(), Box<dyn std::error::Error>>(())
