Adds a faq topic for FastDDS nodes on the same machine, diff users

[wayneparrott]

Public API Changes None

Description Adds a faq topic for configuring FastDDS nodes on the same machine under different users.

817

[coveralls]

Coverage remained the same at 90.544% when pulling 761d8fce45d074e4172f34fed7d00c8830e0dc14 on wayneparrott:doc-update-fastDDS into 5f841743165e25188f01e2fd03ac91db768cf6bc on RobotWebTools:develop.

[wayneparrott]

A quick look at the appveyor log identifies a missing python em package when building the rclnodejs_test_msgs during env setup - see below. This leads to the action tests failing as they try to load msg JS files for the rclnodejs_test_msgs package. Yet it appears the em pkg was installed.

Error msg:

CMake Error at C:/ros2-windows/share/rosidl_adapter/cmake/rosidl_adapt_interfaces.cmake:59 (message):
  execute_process(C:/Python310-x64/python.exe -m rosidl_adapter
  --package-name rclnodejs_test_msgs --arguments-file
  C:/proj/rclnodejs/build/rclnodejs_test_msgs/rosidl_adapter__arguments__rclnodejs_test_msgs.json
  --output-dir
  C:/proj/rclnodejs/build/rclnodejs_test_msgs/rosidl_adapter/rclnodejs_test_msgs
  --output-file
  C:/proj/rclnodejs/build/rclnodejs_test_msgs/rosidl_adapter/rclnodejs_test_msgs.idls)
  returned error code 1:
  Traceback (most recent call last):
    File "C:\Python310-x64\lib\runpy.py", line 196, in _run_module_as_main
      return _run_code(code, main_globals, None,
    File "C:\Python310-x64\lib\runpy.py", line 86, in _run_code
      exec(code, run_globals)
    File "c:\ros2-windows\Lib\site-packages\rosidl_adapter\__main__.py", line 19, in <module>
      sys.exit(main())
    File "c:\ros2-windows\Lib\site-packages\rosidl_adapter\main.py", line 53, in main
      abs_idl_file = convert_to_idl(
    File "c:\ros2-windows\Lib\site-packages\rosidl_adapter\__init__.py", line 18, in convert_to_idl
      from rosidl_adapter.msg import convert_msg_to_idl
    File "c:\ros2-windows\Lib\site-packages\rosidl_adapter\msg\__init__.py", line 16, in <module>
      from rosidl_adapter.resource import expand_template
    File "c:\ros2-windows\Lib\site-packages\rosidl_adapter\resource\__init__.py", line 19, in <module>
      import em
  ModuleNotFoundError: No module named 'em'
Call Stack (most recent call first):
  C:/ros2-windows/share/rosidl_cmake/cmake/rosidl_generate_interfaces.cmake:130 (rosidl_adapt_interfaces)
  CMakeLists.txt:25 (rosidl_generate_interfaces)
-- Configuring incomplete, errors occurred!