quick: add an example (#70)

Fixes #69.

quick/example_test.go

@@ -0,0 +1,19 @@
+package quick_test
+
+import (
+	"log"
+	"os"
+
+	"github.com/alecthomas/chroma/quick"
+)
+
+func Example() {
+	code := `package main
+
+func main() { }
+`
+	err := quick.Highlight(os.Stdout, code, "go", "html", "monokai")
+	if err != nil {
+		log.Fatal(err)
+	}
+}