dockerfile: add comments

Dockerfile

@@ -1,13 +1,19 @@
 FROM golang:alpine
 MAINTAINER Jimmy Zelinskie <jimmyzelinskie@gmail.com>
 
-RUN apk update && apk add curl git
-RUN curl https://glide.sh/get | sh
+# Install OS-level dependencies.
+RUN apk update && \
+    apk add curl git && \
+    curl https://glide.sh/get | sh
 
+# Copy our source code into the container.
 WORKDIR /go/src/github.com/chihaya/chihaya
 ADD . /go/src/github.com/chihaya/chihaya
+
+# Install our golang dependencies and compile our binary.
 RUN glide install
 RUN go install github.com/chihaya/chihaya/cmd/chihaya
 
+# Expose a docker interface to our binary.
 EXPOSE 6880 6881
 ENTRYPOINT ["chihaya"]