cmd/entc: add generate.go file to env init (#402)

* cmd/entc: add generate.go file to env init

* doc: update getting-started and codegen documentation

cmd/entc/entc_test.go

@@ -0,0 +1,35 @@
+// Copyright 2019-present Facebook Inc. All rights reserved.
+// This source code is licensed under the Apache 2.0 license found
+// in the LICENSE file in the root directory of this source tree.
+
+package main
+
+import (
+	"bytes"
+	"os"
+	"os/exec"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestCmd(t *testing.T) {
+	defer os.RemoveAll("ent")
+	cmd := exec.Command("go", "run", "github.com/facebookincubator/ent/cmd/entc", "init", "User")
+	stderr := bytes.NewBuffer(nil)
+	cmd.Stderr = stderr
+	require.NoError(t, cmd.Run(), stderr.String())
+
+	_, err := os.Stat("ent/generate.go")
+	require.NoError(t, err)
+	_, err = os.Stat("ent/schema/user.go")
+	require.NoError(t, err)
+
+	cmd = exec.Command("go", "run", "github.com/facebookincubator/ent/cmd/entc", "generate", "./ent/schema")
+	stderr = bytes.NewBuffer(nil)
+	cmd.Stderr = stderr
+	require.NoError(t, cmd.Run(), stderr.String())
+
+	_, err = os.Stat("ent/user.go")
+	require.NoError(t, err)
+}