Correct location of default clamd.sock file

The change to use /tmp/clamd.sock instead of /var/run/clamd.sock was an intentional 
step towards being able to build an unprivileged/rootless image as requested by 
Cisco-Talos/clamav#478

It looks like we forgot to update the documentation to note the change in the 
clamd.sock location.

README.md

@@ -345,7 +345,7 @@ docker exec --interactive --tty "clamav_container_01" /bin/sh
 ### Unix sockets
 
 The default socket for `clamd` is located inside the container as
-`/run/clamav/clamd.sock` and can be connected to when exposed via a Docker
+`/tmp/clamd.sock` and can be connected to when exposed via a Docker
 volume mount. To ensure, that `clamd` within the container can freely create
 and remove the socket, the path for the socket is to be volume-mounted, to
 expose it for others on the same host to use. The following volume can be used
@@ -357,6 +357,9 @@ open clamd for anyone on the host system.
     --mount type=bind,source=/var/lib/docker/data/clamav/sockets/,target=/run/clamav/
 ```
 
+> _Note_: If you override the `LocalSocket` option with a custom `clamd.conf`
+config file, then you may find the `clamd.sock` file in a different location.
+
 With the socket exposed to the host, any other service can now talk to `clamd`
 as well. If for example `clamdtop` where installed on the local host, calling
 ```bash