configure-dns: Mention DNS IP address

[r3m0t]

File: engine/userguide/networking/configure-dns.md, CC: @mstanleyjones

Should mention the DNS server is always at 127.0.0.11

[shubheksha]

I'll take this one up!

[docker-robott]

Closed issues are locked after 30 days of inactivity.
This helps our team focus on active issues.

If you have found a problem that seems similar to this, please open a new issue.

/lifecycle locked