docs: 📝 update FAQ with details on how to remove old sensors

docs/faq.md

@@ -25,11 +25,23 @@ settings app which can adjust the scaling for the app windows.
 ## Q: What is the resource (CPU, memory) usage of the agent?
 
 Very little in most cases. On Linux, the agent with all sensors working, should
-consume well less than 100 MB of memory with very little CPU usage. Further
+consume well less than 50 MB of memory with very little CPU usage. Further
 memory savings can be achieved by running the agent in “headless” mode with the
 `--terminal` command-line option. This should put the memory usage below 25 MB.
 
 On Linux, many sensors rely on D-Bus signals for publishing their data, so CPU
 usage may be affected by the “business” of the bus. For sensors that are polled
 on an interval, the agent makes use of some jitter in the polling intervals to
 avoid a “thundering herd” problem.
+
+## Q: I've updated the agent and now some sensors have been renamed. I now have a bunch of sensors/entities in Home Assistant I want to remove. What can I do?
+
+Unfortunately, sometimes the sensor naming scheme for some sensors created by
+the agent needs to change. There is unfortunately, no way for the agent to
+rename existing sensors in Home Assistant, so you end up with both the old and
+new sensors showing, and only the new sensors updating.
+
+You can remove the old sensors manually, under Developer Tools->Statistics in
+Home Assistant, for example. The list should contain sensors that are no longer
+"provided" by the agent. Or you can wait until they age out of the Home
+Assistant long-term statistics database automatically.