Add notes about middleware availability per firmware

Author: shamlian

docs/setup/xml-config.md

@@ -2,6 +2,8 @@
 
 ROS 2[^1] is built on top of DDS/RTPS as its middleware, which provides advanced networking features such as: discovery, serialization and transportation.  This **R**OS 2 **m**iddle**w**are is abbreviated **RMW** for short.
 
+The middleware running on the robot can be selected using the [Application Configuration](../webserver/application.md) page on the webserver. Note that the choice of middleware available may be restricted by the firmware installed on your robot; check the [releases](https://github.com/iRobotEducation/create3_docs/releases) for more details on available firmware.
+
 This page contains some examples that may be useful when interacting with the iRobot® Create® 3.
 
 !!! important

docs/webserver/application.md

@@ -26,6 +26,8 @@ Further details on these settings can be found in the official ROS 2 documentati
 For robots running Galactic >= G.4 and Humble >= H.1, when Fast-DDS is selected as the RMW, it is possible to direct the robot to use an offboard Fast-DDS Discovery server, as well.
 Further details on the Fast-DDS Discovery Server can be found [here](https://fast-dds.docs.eprosima.com/en/latest/fastdds/ros2/discovery_server/ros2_discovery_server.html).
 
+When running Create 3 firmware for Iron, only one middleware selection is available at a time; to switch middleware, it is necessary to install the matching firmware.
+
 ### Application ROS 2 Parameters File
 This is a raw yaml file used for configuring ROS 2 parameters.
 The web server will not validate this yaml file; setting it incorrectly may cause the application to fail to start properly.