Updated build to be compatible with Go 1.12

[DavidWatkins]

I had an issue where I could not build on my Raspberry Pi. I also added instructions for creating a service. Some of my URLs are pointing to my repo. I think the way Go handles imports doesn't lend itself well to pull requests? Let me know how I should proceed.

[step21]

Does this NEED go 1.12? Tried it on my raspberry pi 2 with go 1.7 and 1.8. Both give these errors similar to what was reported in another issue.

# github.com/miekg/dns
../go/src/github.com/miekg/dns/dnssec_keyscan.go:260: undefined: strings.Builder
../go/src/github.com/miekg/dns/msg_helpers.go:145: base32.HexEncoding.WithPadding undefined (type *base32.Encoding has no field or method WithPadding)
../go/src/github.com/miekg/dns/msg_helpers.go:145: undefined: base32.NoPadding
../go/src/github.com/miekg/dns/msg_helpers.go:271: undefined: strings.Builder
../go/src/github.com/miekg/dns/serve_mux.go:43: undefined: strings.Builder
../go/src/github.com/miekg/dns/types.go:440: undefined: strings.Builder
../go/src/github.com/miekg/dns/types.go:464: undefined: strings.Builder
../go/src/github.com/miekg/dns/types.go:492: undefined: strings.Builder
../go/src/github.com/miekg/dns/types.go:513: undefined: strings.Builder
../go/src/github.com/miekg/dns/types.go:523: undefined: strings.Builder
../go/src/github.com/miekg/dns/types.go:492: too many errors

The issues of miekg/dns do not seem to have anything about this.