Describe better build pattern (#59)

* "-tags static" makes the package re-distributable without requiring librdkafka on the receiving host

* mention librdkafka requirement in build as well

Author: johnseekins

Dockerfile

@@ -10,7 +10,7 @@ WORKDIR /src/prometheus-kafka-adapter
 ADD . /src/prometheus-kafka-adapter
 
 RUN go test
-RUN go build -o /prometheus-kafka-adapter
+RUN go build -tags static -o /prometheus-kafka-adapter
 
 FROM alpine:3.11
 

README.md

@@ -78,9 +78,11 @@ When deployed in a Kubernetes cluster using Helm and using an external Prometheu
 
 ## development
 
+Building requires librdkafka be available on the building host. It is typically available in distribution package archives, but can also be downloaded and built from here: https://github.com/edenhill/librdkafka.git
+
 ```
 go test
-go build
+go build -tags static
 ```
 
 ## contributing