added a simple readme file to show the usage.

README.rst

@@ -0,0 +1,38 @@
+API Usage
+=========
+
+Create a Xunlei object
+
+    import xunlei
+    xunlei_obj = xunlei.Xunlei(USERNAME, PASSWORD, COOKIE_FILE_PATH)
+
+List Xunlei lixian tasks
+
+    items = xunlei_obj.dashboard()
+
+List a bittorrent task
+
+    items = xunlei_obj.list_bt(url, task_id) # url and task_id are from dashboard() function
+
+Download a task
+
+    xunlei_obj.dowload(url, filename)
+
+Download a task with file size checking and resume
+
+    xunlei_obj.smart_download(url, filename, size)
+
+
+CLI Usage
+=========
+
+Edit config file at `~/xunleirc`, add settings for `username` and `password`
+
+List xunlei tasks
+
+    xunlei_cli dashboard
+
+Download a task
+
+    xunlei_cli download TASK_ID
+