Clarify timeout unit in readme

Docs say 

```
`timeout`: Idle socket timeout. Automatically ends incoming sockets if found idle for this
   duration. Defaults to `30` seconds.
```

The "30 seconds" is misleading, since the unit is actually milliseconds.

I propose:

```
`timeout`: Idle socket timeout in milliseconds. Automatically ends incoming sockets if found idle for this
   duration. Defaults to 30 seconds.
```
