adds dockerfile that uses pipenv

Dockerfile

@@ -0,0 +1,19 @@
+FROM python:3.6-alpine
+
+RUN apk add --update tini
+RUN apk add --update build-base
+RUN apk add --update libffi-dev
+
+ENV PIPENV_VENV_IN_PROJECT=1
+ENV PIPENV_IGNORE_VIRTUALENVS=1
+ENV PIPENV_NOSPIN=1
+ENV PIPENV_HIDE_EMOJIS=1
+
+RUN pip install pipenv
+
+COPY . /
+
+RUN pipenv sync
+
+ENTRYPOINT ["/sbin/tini", "--"]
+CMD ["pipenv", "run", "python", "-m", "bot"]