add Dockerfile

preparation (only necessary if Dockerfile changes):
docker build -t ffpb/build .

usage (example):
docker run --env BRANCH=stable BASE=v2014.4 VERSION=0.6.1 ffpb/build

Dockerfile

@@ -0,0 +1,13 @@
+FROM ubuntu:14.04
+MAINTAINER hej@c3pb.de
+
+RUN apt-get update && apt-get install -y build-essential git python libfaketime libgmp-dev libmpfr-dev libmpc-dev
+RUN git config --global user.email build@paderborn.freifunk.net
+
+RUN mkdir /code
+WORKDIR /code
+
+RUN git clone https://git.c3pb.de/freifunk-pb/firmware.git .
+
+CMD ["/bin/bash", "build.sh"]
+