Fix command hint to generate a config file (#4353)

* Fix command hint to generate a config file

When trying to start Synapse without a config file, it will complain
and give a hint towards what command to run. This hinted command
is missing the "report_stats" parameter, which is required with either
yes or no value. Add this to the command.

Not an ideal situation but makes the given command work without the
user getting another error, even though it might be unclear what
"report_stats" represents.

Signed-off-by: Jason Robinson <jasonr@matrix.org>