add docs for casbin backend Signed-off-by: closetool <c299999999@qq.com>

diff --git a/auth_server/authz/casbin_authz.go b/auth_server/authz/casbin_authz.go
index e66bd10..94ff0d8 100644
--- a/auth_server/authz/casbin_authz.go
+++ b/auth_server/authz/casbin_authz.go

@@ -1,18 +1,16 @@
-/*
-   Copyright 2020 Cesanta Software Ltd.
-
-   Licensed under the Apache License, Version 2.0 (the "License");
-   you may not use this file except in compliance with the License.
-   You may obtain a copy of the License at
-
-       https://www.apache.org/licenses/LICENSE-2.0
-
-   Unless required by applicable law or agreed to in writing, software
-   distributed under the License is distributed on an "AS IS" BASIS,
-   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-   See the License for the specific language governing permissions and
-   limitations under the License.
-*/
+// Copyright 2021 The casbin Authors. All Rights Reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
 
 package authz
 

diff --git a/auth_server/authz/casbin_authz_test.go b/auth_server/authz/casbin_authz_test.go
index 549dfc3..106d805 100644
--- a/auth_server/authz/casbin_authz_test.go
+++ b/auth_server/authz/casbin_authz_test.go

@@ -1,3 +1,17 @@
+// Copyright 2021 The casbin Authors. All Rights Reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
 package authz
 
 import (

diff --git a/docs/casbin_backend.md b/docs/casbin_backend.md
new file mode 100644
index 0000000..44dfe4d
--- /dev/null
+++ b/docs/casbin_backend.md

@@ -0,0 +1,15 @@
+# Casbin Backend
+
+[Casbin](https://github.com/casbin/casbin) is a powerful and efficient open-source access control library written by Golang. It provides support for enforcing authorization based on various access control models.
+
+## Usage
+
+add casbin section in yml configuration file
+
+```yaml
+casbin_authz:
+  model_path: "path/to/model"
+  policy_path: "path/to/policy"
+```
+
+more info see: https://github.com/casbin/casbin
\ No newline at end of file