Added Dockerfile, updated README

Dockerfile

+FROM alpine:3.5
+
+RUN apk add --no-cache ca-certificates
+
+ADD apache_exporter /
+
+EXPOSE 9117
+ENTRYPOINT ["/apache_exporter"]
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README.md

@@ -21,3 +21,20 @@ Help on flags:
 
 Tested on Apache 2.2 and Apache 2.4.
 
+# Using Docker
+
+## Build
+
+Run the following commands from the project root directory.
+
+```
+env GOOS=linux GOARCH=amd64 go build .
+docker build -t apache_exporter .
+```
+
+## Run
+
+```
+docker run -d -p 9117:9117 apache_exporter \
+  -scrape_uri "https://your.server.com/server-status/?auto"
+```
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