added Dockerfile for automated build

scripts/Dockerfile

+FROM debian:jessie 
+MAINTAINER Marek Vavrusa <marek.vavrusa@nic.cz>
+
+# Nprocs
+ENV THREADS 2
+
+# Install dependencies and sources 
+RUN apt-get -y update; \
+apt-get install -y \
+build-essential \
+git-core \
+libtool \
+autoconf \
+flex \
+bison \
+libssl-dev \
+liburcu-dev \
+pkg-config \
+liblmdb-dev; \
+# Fetch sources
+mkdir /src; \
+git clone https://gitlab.labs.nic.cz/labs/knot.git /src/knot; \
+# Compile sources in the right order
+cd /src/knot && autoreconf -if && ./configure && make -j${THREADS} && make install && ldconfig; \
+# Trim down the image
+apt-get clean && rm -rf /var/lib/apt/lists/* /tmp/* /src
+
+# Select entrypoint
+WORKDIR /root
+ENTRYPOINT "/usr/local/sbin/knotd"
+CMD ["--help"]
+
+# Expose port
+EXPOSE 53