Update readme

Author: zhangliang

Diff for: README.md

@@ -15,4 +15,23 @@ SET ZONE=huadong
 SET BUCKET=nameimtest
 SET PREFIX=drone/
 SET PATH=e:\drone-qiniu
+```
+
+## Usage
+```
+steps:
+  - name: upload-static
+    image: bysir/drone-qiniu:master
+    pull: if-not-exists
+    privileged: true
+    settings:
+      access_key:
+        from_secret: qiniu_access_key
+      SECRET_KEY:
+        from_secret: qiniu_secret_key
+      zone: huadong
+      bucket: creght-sys
+      prefix: render/
+      path: ./internal/render/static
+
 ```

Diff for: lib/qiniu/upload.go

@@ -2,6 +2,7 @@ package qiniu
 
 import (
 	"context"
+	"fmt"
 	"os"
 	"path/filepath"
 	"strings"
@@ -26,7 +27,12 @@ type PutRsp struct {
 
 // 上传一个文件夹
 func (u Uploader) UploadDir(zone *storage.Zone, bucket string, keyPrefix string, dirPath string) (err error) {
+	fmt.Printf("upload dir: '%s' to bucket '%s', prefix: '%s'\n", dirPath, bucket, keyPrefix)
+
 	err = filepath.Walk(dirPath, func(path string, info os.FileInfo, err error) error {
+		if err != nil {
+			return err
+		}
 		if info.IsDir() {
 			return nil
 		}