Clarify docstring
Clarify docstring

Co-Authored-By: Richard van der Hoff <6e2e234be92ed8dc85f875dbc2f9b6424da7a211@users.noreply.github.com>
matrix-org/synapse,matrix-org/synapse,matrix-org/synapse,matrix-org/synapse,matrix-org/synapse,matrix-org/synapse