printer: doc for exported symbols

Updates #9

printer/printer_test.go

@@ -0,0 +1,31 @@
+package printer_test
+
+import (
+	"fmt"
+
+	"github.com/mmcloughlin/avo/printer"
+)
+
+func ExampleConfig_GeneratedWarning() {
+	// Default configuration named "avo".
+	cfg := printer.NewDefaultConfig()
+	fmt.Println(cfg.GeneratedWarning())
+
+	// Name can be customized.
+	cfg = printer.Config{
+		Name: "mildred",
+	}
+	fmt.Println(cfg.GeneratedWarning())
+
+	// Argv takes precedence.
+	cfg = printer.Config{
+		Argv: []string{"echo", "hello", "world"},
+		Name: "mildred",
+	}
+	fmt.Println(cfg.GeneratedWarning())
+
+	// Output:
+	// Code generated by avo. DO NOT EDIT.
+	// Code generated by mildred. DO NOT EDIT.
+	// Code generated by command: echo hello world. DO NOT EDIT.
+}