docs: add prelim draft of payload schemas

Author: zenlex

SERVICES.md

@@ -13,6 +13,34 @@ target_port=8080 # the target port for your service
 
 **PR's that do not include documentation of the service will not be merged**
 
+- your service will receive any payload/query params from the initial client request as well as a JWT containing a basic user object with the following schema:
+```json
+{
+  "user":{
+    "username":"github_username",
+    "metadata": {
+      //General User Data TBD
+      "services": {
+        "your-service-name": {
+          //User metadata for your service - 500B max
+        }
+      }
+    }
+  } 
+}
+```
+- To update user metadata, make a POST request to `https://tulsawebdevs.org/api/userdata` with a JSON payload in the following schema:
+ ```json
+{
+  "username":"github_username",
+  "metadata": {
+    // User metadata for your service - 500B max
+  }
+}
+```
+- The API will validate your request, attempt to write the user data if valid,  and return a success or failure status. 
+*TBD: Auth/Validation/Rate Limit rules for this - will likely have a token endpoint and require a bearer token or similar for requests*
+
 ## Registered Services
 *Use the following basic format `[repo link](https://myservicelocation)` - Service Name / short description