feat: add dockerfile for documentation

To be able to generate versionned documentation

docs.Dockerfile

@@ -0,0 +1,10 @@
+FROM alpine:3.7
+
+ENV PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/root/.local/bin
+
+COPY requirements.txt /mkdocs/
+WORKDIR /mkdocs
+VOLUME /mkdocs
+
+RUN apk --no-cache --no-progress add py-pip \
+  && pip install --user -r requirements.txt

requirements.txt

@@ -1,3 +1,3 @@
-mkdocs>=0.16.1
-pymdown-extensions>=1.4
-mkdocs-bootswatch>=0.4.0
+mkdocs>=0.16.1,<0.17.0
+pymdown-extensions==1.4
+mkdocs-bootswatch==0.4.0