Add docker example

Add simple Dockerfile and instructions on how to use it. This is a
good starting point to configure your system.

src/Dockerfile

@@ -0,0 +1,9 @@
+FROM ubuntu:18.04
+
+ENV DEBIAN_FRONTEND=noninteractive
+RUN apt-get update && apt-get dist-upgrade && apt-get -y install python3 python3-pip texlive-latex-base texlive-latex-recommended texlive-fonts-recommended texlive-latex-extra latexmk
+COPY requirements.txt /tmp
+RUN pip3 install -r /tmp/requirements.txt
+VOLUME /tmp/src
+WORKDIR /tmp/src
+CMD make -C b3 html latexpdf

src/README.md

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+WISHBONE Specification Sources
+==============================
+
+Those are the ReStructuredText (RST) sources for the Wishbone
+specification. To build the sources, follow one of the following
+guides.
+
+Using Docker
+------------
+
+Just create the container:
+
+```
+docker build -t wishbone-bld .
+```
+
+Then build the documentation:
+
+```
+docker run -it -v $PWD:/tmp/src wishbone-bld make -C b3 html latexpdf
+```
+
+On your system
+--------------
+
+You can just use your standard Python installation. If you want to
+build the PDF you will need the texlive installtion. On Ubuntu 18.04
+the following should suffice to build the documentation:
+
+```
+apt-get -y install python3 python3-pip texlive-latex-base texlive-latex-recommended texlive-fonts-recommended texlive-latex-extra latexmk
+```
+
+To install the Python dependencies globally:
+
+```
+pip3 install -r requirements.txt
+make -C b3 latexpdf html
+```
+
+The preferred way is to use Python virtual environments (venv):
+
+```
+python3 -m venv .venv
+source .venv/bin/activate
+pip install -r requirements.txt
+make -C b3 latexpdf html
+```