Update docs about realtime thread

example_7/doc/userdoc.rst

@@ -22,7 +22,7 @@ ros2_control introduces ``state_interfaces`` and ``command_interfaces`` to abstr
 
 ros2_control provides the ``ControllerInterface`` and ``HardwareInterface`` classes for robot agnostic control. During initialization, controllers request ``state_interfaces`` and ``command_interfaces`` required for operation through the ``ControllerInterface``. On the other hand, hardware drivers offer ``state_interfaces`` and ``command_interfaces`` via the ``HardwareInterface``. ros2_control ensure all requested interfaces are available before starting the controllers. The interface pattern allows vendors to write hardware specific drivers that are loaded at runtime.
 
-The main program is a realtime read, update, write loop. During the  read call, hardware drivers that conform to ``HardwareInterface`` update their offered ``state_interfaces`` with the newest values received from the hardware. During the update call, controllers calculate commands from the updated ``state_interfaces`` and writes them into its ``command_interfaces``. Finally, during to write call, the hardware drivers read values from their offer ``command_interfaces`` and send them to the hardware. The ``ros2_control`` node runs the main loop a realtime thread. The ``ros2_control`` node runs a second non-realtime thread to interact with ROS publishers, subscribers, and services.
+The main program is a realtime read, update, write loop. During the  read call, hardware drivers that conform to ``HardwareInterface`` update their offered ``state_interfaces`` with the newest values received from the hardware. During the update call, controllers calculate commands from the updated ``state_interfaces`` and writes them into its ``command_interfaces``. Finally, during to write call, the hardware drivers read values from the ``command_interfaces`` and sends them to the hardware. The ``ros2_control_node`` runs the main loop in a realtime thread. The ``ros2_control_node`` runs a second non-realtime thread to interact with ROS publishers, subscribers, and services.
 
 Writing a URDF
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