Add -q0 option to nc in docs

With some versions of nc, the connection is kept open after all data is sent. Using -q0 parameter will make nc quit immediatly after EOF on stdin.

Debian has two debian packages for nc: netcat-traditional and netcat-openbsd. The former hangs after EOF on stdin, whereas the latter quits. I assume the expected behavior is to quit nc after sending the metric data.
Merge pull request #443 from cbliard/patch-2

Add -q0 option to nc in docs