docs(lib): Add some initial module documentation

README.md

 # collective
 
 [![pipeline status](https://gitlab.chromabits.com/etcinit/collective/badges/master/pipeline.svg)](https://gitlab.chromabits.com/etcinit/collective/-/commits/master)
+
+A collection of utilities for building Rust CLI applications and services.

src/lib.rs

+#![doc = include_str!("../README.md")]
+
+/// CLI application utilities.
 pub mod cli;
+/// Configuration retrieval and parsing.
 pub mod config;
+/// Ephemeral working directories.
 pub mod rundir;
+/// String utilities.
 pub mod str;