add; instructions for using docker container and port specification

Author: karthikmuralidharan

.env.template

@@ -1,3 +1,3 @@
 TWILIO_ACCOUNT_SID=ACxxxxxxxxxx
 TWILIO_API_KEY=SKxxxxxxxxxx
-TWILIO_API_SECRET=xxxxxxxxxx
+TWILIO_API_SECRET=xxxxxxxxxx

Dockerfile

@@ -1,7 +1,13 @@
 FROM node:alpine
 
+# Default port is set to 3000. 
+# This will be overriden if a diffferent value is provided as an argument for the container.
+ENV PORT 3000 
+
 RUN apk update
+RUN apk upgrade
 RUN apk add git bash curl wget
+RUN rm -rf /var/cache/apk/*
 
 RUN mkdir -p /usr/src/app
 WORKDIR /usr/src/app
@@ -11,4 +17,3 @@ RUN npm install && npm cache clean --force
 COPY . /usr/src/app
 
 CMD [ "npm", "start" ]
-EXPOSE 3000

README.md

@@ -14,24 +14,27 @@ all the config values we need to run the application:
 ## A Note on API Keys
 
 When you generate an API key pair at the URLs above, your API Secret will only
-be shown once - make sure to save this in a secure location, 
+be shown once - make sure to save this in a secure location,
 or possibly your `~/.bash_profile`.
 
 ## Setting Up The Application
 
 Create a configuration file for your application:
+
 ```bash
 cp .env.template .env
 ```
 
 Edit `.env` with the configuration parameters we gathered from above.
 
 Next, we need to install our dependencies from npm:
+
 ```bash
 npm install
 ```
 
 Now we should be all set! Run the application:
+
 ```bash
 npm start
 ```
@@ -43,6 +46,27 @@ video in both the tabs!
 
 ![screenshot of chat app](https://s3.amazonaws.com/com.twilio.prod.twilio-docs/images/video2.original.png)
 
+## Using Docker
+
+You need to build a docker image with the dependecies installed.
+
+``` bash
+docker build -t video-quickstart-js .
+```
+
+Once the image is created, you can run the container by running the `docker run` command. Replace the
+variables `$HOST_PORT`, `$PORT`.
+
+``` bash
+ docker run -it --rm \
+ -p $HOST_PORT:$PORT \
+ --env-file .env \
+ video-quickstart-js:latest
+```
+
+Add `-d` as an option for running in daemon mode.
+Add `--restart always` options for restarting the container incase of failure or system restart.
+
 ## Examples
 
 The project contains some common use-case examples for the Twilio Video JS SDK.