add upload api doc

docs/UploadApi.md

@@ -0,0 +1,28 @@
+### Upload image by post
+
+- You can upload image by HTTP post with identifier to accesss.
+
+### Post file by `multipart/form-data` 
+
+`Python` demo:
+
+```python
+import requests
+
+url = 'http://localhost/php/index.php'
+
+fields = {
+    'function': 'Photo::add',   # Controller
+    'albumID': 's',  # album id, default s is a public album
+    'identifier': 'change-to-identifier-in-database',
+}
+
+files = {
+    '0': ('file_name.jpg', open('/path/to/file_name.jpg', 'rb')),
+}
+
+response = requests.post(url, files=files, data=fields)
+
+print(response.status_code)
+print(response.text)
+```