doc: improve landing example.

Author: mmaker

src/lib.rs

@@ -19,17 +19,23 @@
 //! # use curve25519_dalek::ristretto::RistrettoPoint;
 //! # use curve25519_dalek::scalar::Scalar;
 //! # use group::Group;
-//!
 //! let mut instance = sigma_rs::LinearRelation::new();
 //! let mut rng = rand::thread_rng();
-//! let witness = vec![Scalar::random(&mut rng), Scalar::random(&mut rng)];
 //!
+//! // Define the proof statement.
 //! let [var_x, var_r] = instance.allocate_scalars();
 //! let [var_G, var_H] = instance.allocate_elements();
 //! instance.allocate_eq(var_G * var_x + var_H * var_r);
 //! instance.set_elements([(var_G, RistrettoPoint::generator()), (var_H, RistrettoPoint::random(&mut rng))]);
+//!
+//! // Assign the image of the linear map.
+//! let witness = vec![Scalar::random(&mut rng), Scalar::random(&mut rng)];
 //! instance.compute_image(&witness);
-//! let narg_string: Vec<u8> = instance.into_nizk(b"your session identifier").unwrap().prove_batchable(&witness, &mut rng).unwrap();
+//!
+//! // Create a non-interactive argument for the instance.
+//! let nizk = instance.into_nizk(b"your session identifier").unwrap();
+//! let narg_string: Vec<u8> = nizk.prove_batchable(&witness, &mut rng).unwrap();
+//! // Print the narg string.
 //! println!("{}", hex::encode(narg_string));
 //! ```
 //!