Fixes #484 by adding MAILGUN_KEY variable to README instructions on setting up .env file, and by adding a default value to the docker-compose environment. (#487)

README.md

@@ -24,7 +24,9 @@ This project is currently in development! It will be announced when there is a (
   S3_BUCKET=<your-s3-bucket>
   GITHUB_ID=<your-github-client-id>
   GITHUB_SECRET=<your-github-client-secret>
+  MAILGUN_KEY=<your-mailgun-api-key>
   ```
+
    If you don't care about being able to upload media files to S3 or Login with Github, you can drop in the file exactly how it is. Or, if you don't want to do that, just ask me to send you mine. Refer to [this gist](https://gist.github.com/catarak/70c9301f0fd1ac2d6b58de03f61997e3) for creating an S3 bucket for testing, or if you don't want to do that, I can add you to one of my S3 buckets.
 
 7. `$ npm run fetch-examples` - this downloads the example sketches into a user called 'p5'
@@ -42,7 +44,7 @@ The automatic redirection to HTTPS is turned off by default in development. If y
 
 Using Docker, you can have a complete, consistent development environment without having to manually install dependencies such as Node, Mongo, etc. It also helps isolate these dependencies and their data from other projects that you may have on the same computer that use different/conflicting versions, etc.
 
-Note that this takes up a significant amount of space on your machine. Make sure you have at least 5GB free. 
+Note that this takes up a significant amount of space on your machine. Make sure you have at least 5GB free.
 
 1. Install Docker for your operating system
    * Mac: https://www.docker.com/docker-mac

docker-compose.yml

@@ -16,6 +16,7 @@ services:
       - S3_BUCKET=override_in_dotenv
       - GITHUB_ID=override_in_dotenv
       - GITHUB_SECRET=override_in_dotenv
+      - MAILGUN_KEY=override_in_dotenv
     volumes:
       - .:/opt/node/app
       - /opt/node/app/node_modules