feat: add Docker support, and documentation for it

Dockerfile

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+FROM node:16
+
+# Create app directory
+WORKDIR /usr/src/app
+
+# Install app dependencies
+# A wildcard is used to ensure both package.json AND package-lock.json are copied
+# where available (npm@5+)
+COPY package*.json ./
+
+# Download, and prepare the kepubify binary
+RUN wget https://github.com/pgaskin/kepubify/releases/download/v4.0.4/kepubify-linux-64bit
+RUN mv kepubify-linux-64bit /usr/local/bin/kepubify
+RUN chmod +x /usr/local/bin/kepubify
+
+COPY . .
+
+EXPOSE 3001
+CMD [ "node", "index" ]