main.rs: documentation update

Signed-off-by: Ralf Zerres <ralf.zerres@networkx.de>

src/main.rs

@@ -1,6 +1,6 @@
 /* advotracker infrastructure.
  *
- * Copyright 2019 Ralf Zerres <ralf.zerres@networkx.de>
+ * Copyright 2020 Ralf Zerres <ralf.zerres@networkx.de>
  * SPDX-License-Identifier: (0BSD or MIT)
  */
 
@@ -8,6 +8,8 @@
 //#![feature(proc_macro)]
 //#![deny(rust_2018_idioms)]
 
+/// advotrackerd: the main binary
+
 //use log::info; //substituted with tracing
 use dotenv::dotenv;
 use locales::t;
@@ -76,6 +78,8 @@ fn run_test(matches: &ArgMatches)  -> Result<(), String> {
 }
  */
 
+/// `advotrackerd` is the daemon that keeps track of legal mandate data
+/// that are backed up in a database.
 fn main() -> Result<(), Box<dyn std::error::Error>> {
     use parse_args::parse_args;
     use tracing_subscriber::fmt;
@@ -86,6 +90,8 @@ fn main() -> Result<(), Box<dyn std::error::Error>> {
     //    .expect("setting tracing default failed");
 
     // initialize the tracing subsystem
+    // a drop in replacement for classical logging
+    // reference: https://tokio.rs/blog/2019-08-tracing/
     let span = tracing::span!(Level::TRACE, "advotracker_main");
     let _enter = span.enter();
     let subscriber = fmt::Subscriber::builder()