Add docker things for documentation

docs.Dockerfile

@@ -0,0 +1,11 @@
+FROM alpine
+
+ENV PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/root/.local/bin
+
+COPY requirements.txt /mkdocs/
+WORKDIR /mkdocs
+
+RUN apk --update upgrade \
+&& apk --no-cache --no-progress add py-pip \
+&& rm -rf /var/cache/apk/* \
+&& pip install --user -r requirements.txt