Match lib.rs doc comments to README.md.

src/lib.rs

@@ -1,17 +1,25 @@
-//! # Roundable values
+//! # Round numbers and durations to a given factor
 //!
 //! This provides an implementation of rounding for various values, including
-//! [`core::time::Duration`] (or `std::time::Duration`).
+//! the the native number types and [`core::time::Duration`] (or
+//! `std::time::Duration`).
+//!
+//! This crate is does not need `std` or `alloc` (it’s always in `no_std` mode).
+//! No features need to be enabled or disabled.
 //!
 //! ```rust
 //! use roundable::Roundable;
 //!
 //! assert!(310 == 314.round_to(10));
 //! assert!(300.0 == 314.1.round_to(100.0));
+//!
+//! // To avoid panicking on overflow:
+//! assert!(Some(260) == 255.try_round_to(10));
+//! assert!(None == 255u8.try_round_to(10));
 //! ```
 //!
-//! See [Constants](#constants) for a list of time units that make rounding
-//! [`Duration`] easier.
+//! See [the list of constants][#constants] for a list of time units that make
+//! rounding [`Duration`] easier.
 //!
 //! ```rust
 //! use roundable::{SECOND, MINUTE, Roundable};