add a Dockerfile

Thanks to @jarededwards

Dockerfile

@@ -0,0 +1,11 @@
+FROM node:20-alpine3.17
+
+WORKDIR /
+
+COPY . .
+
+RUN npm install
+
+EXPOSE 8080
+
+CMD ["node", "index.js"]

README.md

@@ -25,8 +25,19 @@ First, you need to run the application on a cloud provider: you could run it loc
 
 _Future versions of this app will probably use templating, so this stupid implementation of `WELCOME_PART1` & `WELCOME_PART2` will be things of the past._
 
+#### Run
+
 Once it's done, you can run the application using the `node index.js` command. You would be advised to run it as a service to ensure it's always running, and restart when there is an issue (running it with something like [pm2](https://github.com/Unitech/pm2) `pm2 start index.js`). Note that the app won't work at first as you need to update the other variables from the [.env file](.env)), but you won't be able to do it before you create the Slack application.
 
+#### Docker
+
+You can also run the application using Docker
+
+```shell
+docker build -t warm-welcome .
+docker run -p 80:8080 warm-welcome
+```
+
 ### Slack Application
 
 First, you need to create a new Slack application. To do so, connect to your Slack Workspace in the browser, and go to [Your Apps](https://api.slack.com/apps). Click on the `Create an app` button, and choose the second option named `From an app manifest`. On step 1 of 3 screens, pick the workspace you want to welcome people, and click `Next`.