docs: adjust code block indent (#11)

Author: Zeeland

README.md

@@ -34,20 +34,20 @@ MIDDLEWARE = [
 ```python
 import casbin
 
-    def __init__(self, get_response):
-        self.get_response = get_response
-        # load the casbin model and policy from files.
-        # change the 2nd arg to use a database.
-        self.enforcer = casbin.Enforcer("casbin_middleware/authz_model.conf", "casbin_middleware/authz_policy.csv")
-
-    def check_permission(self, request):
-        # change the user, path, method as you need.
-        user = request.user.username
-        if request.user.is_anonymous:
-            user = 'anonymous'
-        path = request.path
-        method = request.method
-        return self.enforcer.enforce(user, path, method)
+def __init__(self, get_response):
+    self.get_response = get_response
+    # load the casbin model and policy from files.
+    # change the 2nd arg to use a database.
+    self.enforcer = casbin.Enforcer("casbin_middleware/authz_model.conf", "casbin_middleware/authz_policy.csv")
+
+def check_permission(self, request):
+    # change the user, path, method as you need.
+    user = request.user.username
+    if request.user.is_anonymous:
+        user = 'anonymous'
+    path = request.path
+    method = request.method
+    return self.enforcer.enforce(user, path, method)
 ```
 
 - The default policy ``authz_policy.csv`` is: