Add configuration through environment variables (#456)

Author: Zertz

README.md

@@ -44,6 +44,9 @@ After starting the dashboard, you can visit http://localhost:4040 in your browse
 ![Parse Dashboard](.github/dash-shot.png)
 
 ## Configuring Parse Dashboard
+
+### File
+
 You can also start the dashboard from the command line with a config file.  To do this, create a new file called `parse-dashboard-config.json` inside your local Parse Dashboard directory hierarchy.  The file should match the following format:
 
 ```json
@@ -61,6 +64,34 @@ You can also start the dashboard from the command line with a config file.  To d
 
 You can then start the dashboard using `parse-dashboard --config parse-dashboard-config.json`.
 
+### Environment variables
+
+There are also two methods you can use to configure the dashboard using environment variables.
+
+#### Multiple apps
+
+Provide the entire JSON configuration in `PARSE_DASHBOARD_CONFIG` and it will be parsed just like the config file.
+
+#### Single app
+
+You can also define each configuration option individually.
+
+```
+HOST: "0.0.0.0"
+PORT: "4040"
+MOUNT_PATH: "/"
+PARSE_DASHBOARD_ALLOW_INSECURE_HTTP: undefined // Or "1" to allow http
+PARSE_DASHBOARD_SERVER_URL: "http://localhost:1337/parse"
+PARSE_DASHBOARD_MASTER_KEY: "myMasterKey"
+PARSE_DASHBOARD_APP_ID: "myAppId"
+PARSE_DASHBOARD_APP_NAME: "MyApp"
+PARSE_DASHBOARD_USER_ID: "user1"
+PARSE_DASHBOARD_USER_PASSWORD: "pass"
+PARSE_DASHBOARD_SSL_KEY: "sslKey"
+PARSE_DASHBOARD_SSL_CERT: "sslCert"
+PARSE_DASHBOARD_CONFIG: undefined // Only for reference, it must not exist
+```
+
 ## Managing Multiple Apps
 
 Managing multiple apps from the same dashboard is also possible.  Simply add additional entries into the `parse-dashboard-config.json` file's `"apps"` array.