Add example

README.md

@@ -1,3 +1,44 @@
 # go-eta
 
 ETA calculator for Go.
+
+## Example
+
+```go
+package main
+
+import (
+	"fmt"
+	"math/rand"
+	"os"
+	"time"
+
+	"github.com/nxshock/go-eta"
+)
+
+func main() {
+	stepsCount := 1000
+
+	eta := eta.New(time.Minute, stepsCount)
+
+	processed := 0
+
+	// Emulate work
+	go func() {
+		for processed < stepsCount {
+			time.Sleep(time.Second)
+			r := rand.Intn(30)
+
+			processed += r
+			eta.Increment(r)
+		}
+	}()
+
+	// Print progress
+	for processed < stepsCount {
+		time.Sleep(time.Second) // Update progress every second
+		fmt.Fprintf(os.Stderr, "\rProcessed %d of %d, ETA: %s", processed, stepsCount, eta.Eta().Format("15:04:05"))
+	}
+
+}
+```