Update README.md

README.md

@@ -21,7 +21,7 @@ func main() {
 	schedule, err := crong.New("0 0 * * *", time.UTC)
 	if err != nil {
 		log.Fatal(err)
-    }
+    	}
 
 	// Get the next (or most recent) scheduled time relative to the given time
 	fmt.Println("Next scheduled time:", schedule.Next(time.Now()))
@@ -30,7 +30,7 @@ func main() {
 	// Check if the given time satisfies the schedule
 	if schedule.Matches(time.Now()) {
 		fmt.Println("It's time!")
-    }
+    	}
 }
 ```
 
@@ -51,15 +51,15 @@ func main() {
 	schedule, err := crong.New("@hourly", time.UTC)
 	if err != nil {
 		log.Fatal(err)
-    }
+    	}
 
 	ticker := crong.NewTicker(context.Background(), schedule, 1 * time.Minute)
 	defer ticker.Stop()
 
 	select {
 	case t := <-ticker.C:
 		log.Printf("%s: Tick!", t)
-    }
+    	}
 }
 ```
 
@@ -79,7 +79,7 @@ func main() {
 	schedule, err := crong.New("* * * * *", time.UTC)
 	if err != nil {
 		log.Fatal(err)
-    }
+    	}
 
 	// MaxConcurrent=0 only allows the job to run sequentially, while
 	// increasing TickerReceiveTimeout can accommodate potentially long-running
@@ -98,8 +98,37 @@ func main() {
 		func(t time.Time) error {
 			log.Printf("Scheduled run for %s started at %s", t, time.Now())
 			return nil
-        },
-    )
+        	},
+	)
 	defer scheduledJob.Stop(context.Background())
 }
 ```
+
+## Syntax
+
+Supports standard cron syntax (see https://en.wikipedia.org/wiki/Cron), as well as less standard expressions. 
+For example, `5/10 4,5 * *` means "every 10 minutes starting at the 5th minute of the hour, for hours 4 and 5."
+
+Days of the week are indexed 0-6, with 0 being Sunday, and can be referenced by 
+name (SUN, MON, TUE, WED, THU, FRI, SAT) or by number.
+
+Months are indexed 1-12, and can be referenced by name 
+(JAN, FEB, MAR, APR, MAY, JUN, JUL, AUG, SEP, OCT, NOV, DEC) or by number.
+
+Cron macros supported:
+
+  - `@yearly` (or `@annually`) - Run once a year, midnight, Jan. 1
+  - `@monthly` - Run once a month, midnight, first of month
+  - `@weekly` - Run once a week, midnight between Saturday and Sunday
+  - `@daily` (or `@midnight`) - Run once a day, midnight
+  - `@hourly` - Run once an hour, beginning of hour
+
+Other characters supported:
+
+  - `*`: Wildcard/Any value (ex: Every minute: `* * * * *`)
+  - `,`: Value list separator (ex: Minute 0 and 30 of every hour: `0,30 * * * *`)
+  - `-`: Range of values (ex: Minute 0-15 of every hour: `0-15 * * * *`)
+  - `/`: Step values (ex: Every 2nd minute from minute 10-20 of every hour: `10-20/2 * * * *`)
+  - `?`: No specific value (month, day of month, day of week only)
+  - `L`: Last day of month. When used, must be used alone in the day
+    field (ex: 12:30 on the last day of every month: `30 12 L * *`)