add Dockerfile based on @promasu 's work

Dockerfile

@@ -0,0 +1,51 @@
+# Multistage build to reduce image size and increase security
+FROM node:lts-alpine AS build
+
+# Install requirements to clone repository and install deps
+RUN apk add --no-cache git
+RUN npm install -g bower
+
+# Create folder for cryptpad
+RUN mkdir /cryptpad
+WORKDIR /cryptpad
+
+# Get cryptpad from repository submodule
+COPY . /cryptpad
+
+RUN sed -i "s@//httpAddress: '::'@httpAddress: '0.0.0.0'@" /cryptpad/config/config.example.js
+RUN sed -i "s@installMethod: 'unspecified'@installMethod: 'docker-alpine'@" /cryptpad/config/config.example.js
+
+# Install dependencies
+RUN npm install --production \
+    && npm install -g bower \
+    && bower install --allow-root
+
+# Create actual cryptpad image
+FROM node:lts-alpine
+
+# Create user and group for cryptpad so it does not run as root
+RUN addgroup -g 4001 -S cryptpad \
+    && adduser -u 4001 -S -D -g 4001 -H -h /cryptpad cryptpad
+
+# Copy cryptpad with installed modules
+COPY --from=build --chown=cryptpad /cryptpad /cryptpad
+USER cryptpad
+
+# Set workdir to cryptpad
+WORKDIR /cryptpad
+
+# Create directories
+RUN mkdir blob block customize data datastore
+
+# Volumes for data persistence
+VOLUME /cryptpad/blob
+VOLUME /cryptpad/block
+VOLUME /cryptpad/customize
+VOLUME /cryptpad/data
+VOLUME /cryptpad/datastore
+
+# Ports
+EXPOSE 3000 3001
+
+# Run cryptpad on startup
+CMD ["npm", "start"]