Added datastore segments docs.newrelic.com link
[SQLDriverSegmentBuilder](https://godoc.org/github.com/newrelic/go-agent#SQLDriverSegmentBuilder).
The integration packages act as examples of how to do this.
+ For more information, see the [Go agent documentation on instrumenting datastore segments](https://docs.newrelic.com/docs/agents/go-agent/instrumentation/instrument-go-segments#go-datastore-segments).
+
### Bug Fixes
* The [http.RoundTripper](https://golang.org/pkg/net/http/#RoundTripper) returned
