Add CLI module documentation

src/main.rs

@@ -1,11 +1,9 @@
-//! Command-line interface for the `mdtablefix` tool.
+//! Command-line interface for `mdtablefix`.
 //!
-//! This module provides the main entry point for the command-line parsing in
-//! the `mdtablefix` crate. It fixes Markdown table formatting and processes
-//! multiple files concurrently using the `rayon` crate. Each worker buffers
-//! its output so lines can be printed in the same order the paths were
-//! supplied. For many small files, this coordination cost may outweigh the
-//! benefits of parallelism.
+//! Parses command-line arguments and coordinate file processing. When paths are
+//! supplied, each file can be rewritten in place and processing is
+//! parallelized with Rayon. Without paths the tool reads from standard input.
+//! Output always appears in the same order as the paths are provided.
 
 use std::{
     borrow::Cow,