Incomplete documentation for sbuftimeout

There are a few things wrong with `sbuftimeout`'s [documentation](https://github.com/bloomberg/comdb2/blob/0c60def2311f710001c272ac56377001690f1e37/docs/pages/config/config_files.md#L762):
* It reads "Set a timeout on client connections, connections drop if they", which is clearly incomplete.
* It doesn't mention the unit of measurement for the timeout (the [source code](https://github.com/bloomberg/comdb2/blob/d53762e59b849ee70c1149258170d4ae73cfb26f/bdb/attr.h#L76) indicates that would be seconds).
* It doesn't explain what the default "not set" value means wrt to that timeout (eg: no/0 timeout, infinite timeout, some other value?).