added example program for testing

example/main.go

@@ -0,0 +1,24 @@
+package main
+
+import (
+	"github.com/glebarez/sqlite"
+	"github.com/wisplite/tether"
+	"gorm.io/gorm"
+)
+
+func main() {
+	db, err := gorm.Open(sqlite.Open("test.db"), &gorm.Config{})
+	if err != nil {
+		panic("failed to connect database")
+	}
+
+	engine := tether.NewEngine(db)
+
+	engine.RegisterMutation("createUser", func(ctx *tether.MutationCtx) error {
+		return nil
+	})
+
+	engine.RegisterQuery("getUser", func(ctx *tether.QueryCtx) error {
+		return nil
+	})
+}