Add properties and metaprotocol to API docs (#4426)

Author: casey

docs/src/guides/api.md

@@ -1354,10 +1354,24 @@ curl -s -H "Accept: application/json" /
   "fee": 322,
   "height": 767430,
   "id": "6fb976ab49dcec017f1e201e84395983204ae1a7c2abf7ced0a85d692e442799i0",
+  "metaprotocol": "LOL-420",
   "next": "26482871f33f1051f450f2da9af275794c0b5f1c61ebf35e4467fb42c2813403i0",
   "number": 0,
   "parents": [],
   "previous": null,
+  "properties": {
+    "gallery": [
+      {
+        "id": "ab924ff229beca227bf40221faf492a20b5e2ee4f084524c84a5f98b80fe527fi0",
+        "attributes": {
+          "title": "goodbye"
+        }
+      }
+    ],
+    "attributes": {
+      "title": "hello"
+    }
+  },
   "rune": null,
   "sat": null,
   "satpoint": "47c7260764af2ee17aa584d9c035f2e5429aefd96b8016cfe0e3f0bcf04869a3:0:0",