Add schema example for post https://stackoverflow.com/a/65150457/687896

Author: chbrandt

docs/address.schema.json

@@ -0,0 +1,8 @@
+{
+  "type": "object",
+
+  "properties": {
+    "billing_address": { "$ref": "definitions.schema.json#" },
+    "shipping_address": { "$ref": "definitions.schema.json#" }
+  }
+}

docs/base.schema.json

@@ -0,0 +1,3 @@
+{
+  "$schema": "http://json-schema.org/draft-07/schema#"
+}

docs/definitions.schema.json

@@ -0,0 +1,9 @@
+{
+  "type": "object",
+  "properties": {
+    "street_address": { "type": "string" },
+    "city":           { "type": "string" },
+    "state":          { "type": "string" }
+  },
+  "required": ["street_address", "city", "state"]
+}