Updates Graph API with Assumptions section

docs/clmc-service.md

@@ -37,6 +37,13 @@ It offers different API endpoints to configure and control the aggregator as wel
 
 #### Graph API Endpoints
 
+* **Assumptions**
+    * For each service function, there is a field/fields from which the service function response time (service delay) can be derived.
+    * For each service function, there is a field/fields from which an average estimation of the size of a **request** to this service function can be derived.
+    * For each service function, there is a field/fields from which an average estimation of the size of a **response** from this service function can be derived.
+    * All the aforementioned fields reside in a single measurement.
+    * There is at most 1 service function hosted on a particular endpoint.
+
 * **POST** ***/graph/temporal?from={timestamp-seconds}&to={timestamp-seconds}***
 
     This API method sends a request to the CLMC service to build a graph related to the time range declared with the *from* and *to* URL parameters.