This is due to the fact that `gh completion` can be programatically used
during shell startup and we definitely don't want to
1. slow down people's startup time
2. show any upgrade notice until the user has invoked `gh` manually
For `net.DNSError`, the full error message can be scary. Instead, print "error
connecting to HOST" and hint that the user should check their internet connection
or githubstatus.com.
When $DEBUG is set, the full DNS error is printed like before.
Fixes#206
`make site-docs`:
1. checks out the `gh-pages` branch into the `site/` directory;
2. regenerates `.md` help pages using Cobra;
3. commits and publishes updates.
