Add test deploy via docker, update README

Author: stefanhoth

README.md

@@ -47,6 +47,13 @@ When you push to github, the official site at http://opentechschool.github.io/py
 
 To generate and view the site (with correct CSS, etc.) with your on your local computer, you can install Jekyll and then run it like this:
 
+If you have [docker installed on your system](https://docs.docker.com/get-docker/) the easiest way to test the site locally is by running
+`./testlocal.sh`
+
+It will download a suitable docker image for jekyll and run the code within this container, making it available via http://localhost:4000/python-data-intro/
+
+Alternatively, you can run the following steps manually:
+
     jekyll --serve --auto
     # or
     jekyll serve --watch

testlocal.sh

@@ -0,0 +1,9 @@
+#!/bin/sh
+
+# run local jekyll server; will be served at localhost:4000
+export JEKYLL_VERSION=3.8
+docker run --rm \
+  --volume="$PWD:/srv/jekyll" -p 4000:4000 \
+  --env JEKYLL_UID=$(id -u) --env JEKYLL_GID=$(id -g) \
+  -it jekyll/jekyll:$JEKYLL_VERSION \
+  jekyll serve --future --drafts