docs: def add_runnable(self, runnable):
          """
          Adds a runnable component to the list of runnable components in
          this simulation.
  
          @param runnable: A runnable component
          @type runnable: lems.sim.runnable.Runnable
          """
  
          if runnable.id in self.runnables:
              raise SimError('Duplicate runnable component {0}'.format(runnable.id))
  
          self.runnables[runnable.id] = runnable