heroku steps added (GoogleChrome#336)

docs/deploy.md

@@ -23,3 +23,56 @@ Rendertron runs a server that takes a URL and returns static HTML for the URL by
 * Enter YOUR_PROJECT_ID.appspot.com in your browser. Replace YOUR_PROJECT_ID with your actual project ID that you set in Google Cloud Platform. You should see Rendertron's interface with an input field and a few buttons.
 
 * When you see the Rendertron web interface, you have successfully deployed your own Rendertron instance. Take note of your project's URL (YOUR_PROJECT_ID.appspot.com) as you will need it later.
+
+
+###  Deploying Rendertron to Heroku
+
+Setup Herokuapp and Heroku CLI
+`https://devcenter.heroku.com/articles/heroku-cli`
+
+First, add the Google Chrome buildpack to your project:
+
+```
+$ heroku buildpacks:set https://github.com/heroku/heroku-buildpack-google-chrome.git -a <app-name>
+```
+
+Next, add the `heroku/nodejs` buildpack to your project:
+
+```
+$ heroku buildpacks:add heroku/nodejs -a <app-name>
+```
+
+Then, update the `package.json` entry for `engines` to specific node and npm versions. I used:
+
+```
+{
+  ...
+  "engines": {
+    "node": "10.15.1",
+    "npm": "6.4.1"
+  },
+  ...
+}
+```
+
+This was helpful in getting past a `node-gyp` issue during `npm install`, which Heroku will run each time you deploy.
+
+Next, enter a new script into your `package.json`:
+
+```
+{
+  "scripts": {
+    ...,
+    "heroku-postbuild": "npm run build"
+  }
+}
+```
+
+This will make sure to build rendertron into `bin/rendertron` on each deploy, in case you have any local changes.
+
+Finally, add a `Procfile` to your project with the following:
+
+```
+web: node bin/rendertron
+```
+