doc: Small notes for resource limiting (#792)

doc/content/reference/resource-limiting/_index.md

@@ -15,7 +15,7 @@ The resource limiting configuration is split into multiple profiles. For each pr
 
 Enable resource limiting by adding the following configuration to your `ttn-lw-stack.yml`.
 
-The values shown below are only meant as an example. Make sure to adjust them accordingly, depending on the actual traffic of your deployment.
+Resource limiting can be applied per application, as well as for all applications in a tenant. The values shown below are only meant as an example. Make sure to adjust them accordingly, depending on the actual traffic of your deployment.
 
 ```yaml
 resource-limiting:
@@ -50,6 +50,8 @@ The following table describes how {{% tts %}} reacts when the maximum resource l
 | gRPC Application Connections | Calls to `Subscribe` RPC will fail with an error of type `ResourceExhausted`. | Terminate existing connections and retry. |
 | MQTT Application Connections | A `ServerUnavailable` response is returned for new connections.               | Terminate existing connections and retry. |
 
+For example, if an MQTT connection is failing due to resource limits exceeding, you will see an error such as `Resource limit 16 exceeded for resource with key as:conn:frontend:mqtt:app:test-app-1@test-tenant-1`. The resolution would be to terminate existing connections and retry.
+
 ## External configuration
 
 It is possible to load extra resource limiting profiles from an external file. Create a file named `/opt/config/resource-limiting.yml` (replace `/opt/config` with any path you like) with the following contents: