Added docker instructions

[dilshavijay]

Explanation of the Dockerfile:
FROM node:18: This specifies the base image. We are using the official Node.js image from Docker Hub with Node version 18.

WORKDIR /usr/src/app: Sets the working directory inside the container. All subsequent commands will run in this directory.

COPY package.json ./**: Copies the package.json and package-lock.json files to the container. The wildcard () is used to match both package.json and package-lock.json files.

RUN npm install --production: Installs only the production dependencies listed in the package.json.

COPY . .: Copies the rest of the application code into the container.

EXPOSE 8080: Informs Docker that the container listens on port 8080 at runtime.

CMD ["node", "app.js"]: Specifies the command to run the application inside the container.