Add bin using crate cron.

src/bin/using-crate-cron.rs

@@ -0,0 +1,13 @@
+use chrono::Utc;
+use cron::Schedule;
+use std::str::FromStr;
+
+fn main() {
+    //               sec  min   hour   day of month   month   day of week   year
+    let expression = "0   30   9,12,15     1,15       May-Aug  Mon,Wed,Fri  2018/2";
+    let schedule = Schedule::from_str(expression).unwrap();
+    println!("Upcoming fire times:");
+    for datetime in schedule.upcoming(Utc).take(10) {
+        println!("-> {}", datetime);
+    }
+}