Doc: Document panic on input bytes more than 2*(2^64-1).
//! - `reset()` is called with `None` as `secret_key` but the struct was
//! initialized with `Some(secret_key)`.
//!
+//! # Panics:
+//! A panic will occur if:
+//! - More than 2*(2^64-1) bytes of data are hashed.
+//!
//! # Security:
//! - The secret key should always be generated using a CSPRNG.
//! `SecretKey::generate()` can be used
