Add docker-compose.yml to ease development

If you have docker and docker-compose installed, you can simply run
docker-compose up in the project directory to fire up the site inside
a Docker container.

docker-compose.yml

@@ -0,0 +1,8 @@
+jekyll:
+    image: jekyll/jekyll:pages
+    command: jekyll serve --livereload --reload_port 35729
+    ports:
+        - 4000:4000
+        - 35729:35729
+    volumes:
+        - .:/srv/jekyll