Add section about logging

[agorgl]

Currently, the book mentions that babashka includes clojure.tools.logging and timbre for logging.
Adding an example usage, would be a nice addition:

#!/usr/bin/env bb
(ns script
  (:require
   [clojure.tools.logging :as log]
   [taoensso.timbre :as timbre]))

(defn -main [& args]
  (log/info "Hello there"))

(when (= *file* (System/getProperty "babashka.file"))
  (apply -main *command-line-args*))

; vim: set ft=clojure:

We should also mention, that because timbre does a dns call to resolve the hostname, the hostname must exist in /etc/hosts to avoid slow (5sec) startup times:

# Static table lookup for hostnames.
# See hosts(5) for details.
127.0.0.1        localhost <your-hostname>
::1              localhost <your-hostname>