add: alpine dockerfile

Dockerfile.alpine

@@ -0,0 +1,22 @@
+FROM node:11-alpine
+
+# copy config, which changes rarely
+COPY docs/config-docker.yml /root/.salty-dog.yml
+
+# copy package first, to invalidate other layers when version changes
+COPY package.json /salty-dog/package.json
+
+# copy chunks, largest to smallest (entrypoint)
+COPY out/vendor.js /salty-dog/out/vendor.js
+COPY out/main.js /salty-dog/out/main.js
+COPY out/index.js /salty-dog/out/index.js
+
+# set up as global cli tool
+WORKDIR /salty-dog
+RUN yarn global add file:$(pwd)
+ENV PATH="${PATH}:$(yarn global bin)"
+
+COPY rules /salty-dog/rules
+
+ENTRYPOINT [ "node", "/salty-dog/out/index.js" ]
+CMD [ "--help" ]