docker: Add Debian image with basic build environment

By running "./make.sh docker" the current build environment
will be mounted into a Debian-based docker container.

This clean build environment can be used to compile the
toolchain or something...

Signed-off-by: Michael Tremer <michael.tremer@ipfire.org>

tools/docker/Dockerfile

@@ -0,0 +1,21 @@
+# This image is based on the latest stable version of Debian
+FROM debian:stable
+
+# Install all updates
+RUN apt-get update && apt-get dist-upgrade
+
+# Install all packages needed for the build
+RUN apt-get install -y \
+	build-essential \
+	autoconf \
+	automake \
+	bison \
+	flex \
+	gawk \
+	git \
+	libz-dev
+
+# Enable colors in git
+RUN git config --global color.ui auto
+
+WORKDIR ~