boilerplate: add .dir-locals.el with emacs python enviroment

The .dir-locals.el set the project's python enviroment for the emacs tasks like
flycheck or jedi.  The py-environment has to be next to <repo>/.dir-locals.el::

    ./local/py3

To setup such an environment build target 'pyenv' or 'pyenvinstall'::

  $ make pyenvinstall

TL;DR

Alternatively create the virtualenv, source it and install jedi + epc
(required by `emacs-jedi <https://tkf.github.io/emacs-jedi

>`_)::

    $ virtualenv --python=python3  "--no-site-packages" ./local/py3
    ...
    $ source ./local/py3/bin/activate
    (py3)$ # now install into the activated 'py3' environment ..
    (py3)$ pip install jedi epc
    ...

Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>