Docker support.

pls confirm  this pr, thk.

and I think we should develp more feature about webhook.     Not only support cmd.
such as, support  webhook module ，sync to database，  http request  or other.

Dockerfile

@@ -0,0 +1,13 @@
+FROM golang:latest
+
+MAINTAINER Dean dean@airdb.com
+# github webhook:  github.com/adnanh/webhook
+
+ENV PATH="$PATH:/go/bin"
+RUN go get github.com/adnanh/webhook
+
+RUN cd /go/src/github.com/adnanh/webhook
+
+ENTRYPOINT webhook  -verbose -hooks ./hooks.json.example
+
+EXPOSE 9000