Update README
net/mosquitto: Import 1.3.1 from packages

This is actively maintained, and will continue to be maintained.

Upstream development versions of the package is available at
https://github.com/remakeelectric/owrt_pub_feeds

Signed-off-by: Karl Palsson <karlp@remake.is>
Merge pull request #1 from remakeelectric/mosquitto

net/mosquitto: Import 1.3.1 from packages