message: Add to ECSQL frontend docs
diff: ECSQL by itself is described in detail here: [ECSQL](../learning/ECSQL)
  -An ECSQL query is executed by calling [IModelConnection.executeQuery]($imodeljs-frontend.IModelConnection.executeQuery).
  +A frontend ECSQL query is executed by calling [IModelConnection.executeQuery]($imodeljs-frontend.IModelConnection.executeQuery).
  -> For iModels. only ECSQL SELECT statements can be executed. Data modification must be done through
  -> the dedicated Element API.
  +> On the frontend, only ECSQL SELECT statements can be executed. Data modification must be done through the API.
  ## ECSQL Parameter Values
  @@ -21,3 +20,9 @@ The section ["iModelJs Types used in ECSQL Parameter Bindings"](../learning/ECSQ
  ## Query Result
  The result of the query is returned as an array of JavaScript objects where every array element represents an [ECSQL row](../learning/ECSQLRowFormat).
  +
  +## Avoid *Chatty* Patterns
  +
  +An ECSQL query initiated from the frontend necessarily requires a round trip with the backend server.
  +In Web Apps, round trips mean exposure to network latency, so a *chunky* request pattern will perform better than a *chatty* request pattern.
  +If multiple queries are required to build up the desired result, consider moving the operation to the backend.
  