Setup local docker-based development environment

docker-entrypoint.sh

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+#!/bin/bash
+set -e
+
+if [ ! -f Gemfile ]; then
+  echo "NOTE: hmm, I don't see a Gemfile so I don't think there's a jekyll site here"
+  echo "Either you didn't mount a volume, or you mounted it incorrectly."
+  echo "Be sure you're in your jekyll site root and use something like this to launch"
+  echo ""
+  echo "docker run -p 4000:4000 -v \$(pwd):/site bretfisher/jekyll-serve"
+  echo ""
+  echo "NOTE: To create a new site, you can use the sister image bretfisher/jekyll like:"
+  echo ""
+  echo "docker run -v \$(pwd):/site bretfisher/jekyll new ."
+  exit 1
+fi
+
+bundle install --retry 5 --jobs 20
+
+exec "$@"