added doc for reverse_interface_addresses cache value format

README.md

@@ -744,3 +744,55 @@ Any non-empty responses are JSON formatted messages.
         "additionalProperties": False
     }
     ```
+
+* `reverse_interface_addresses/<address>`
+  * key examples
+    * `reverse_interface_addresses:193.203.0.203`
+    * `reverse_interface_addresses:2001:07f8:00a0:0000:0000:5926:0000:0002`
+  * valid values:
+    ```json
+    {
+        "$schema": "http://json-schema.org/draft-07/schema#",
+
+        "definitions": {
+            "v4a": {
+                "type": "string",
+                "pattern": r'^(\d+\.){3}\d+$'
+            },
+            "v6a": {
+                "type": "string",
+                "pattern": r'^([a-f\d]{4}:){7}[a-f\d]{4}$'
+            },
+            "v4i": {
+                "type": "string",
+                "pattern": r'^(\d+\.){3}\d+/\d+$'
+            },
+            "v6i": {
+                "type": "string",
+                "pattern": r'^[a-f\d:]+/\d+$'
+            }
+        },
+
+        "type": "array",
+        "items": {
+            "type": "object",
+            "properties": {
+                "name": {
+                    "oneOf": [
+                        {"$ref": "#/definitions/v4a"},
+                        {"$ref": "#/definitions/v6a"}
+                    ]
+                },
+                "interface address": {
+                    "oneOf": [
+                        {"$ref": "#/definitions/v4i"},
+                        {"$ref": "#/definitions/v6i"}
+                    ]
+                },
+                "interface name": {"type": "string"},
+            },
+            "required": ["name", "interface address", "interface name"],
+            "additionalProperties": False
+        }
+    }
+    ```