Update example with known env vars

Sanitised by removing passwords and users where appropriate.

.env.example

@@ -1,8 +1,71 @@
+
+# Passenger
+PASSENGER_MAX_POOL_SIZE=5
+
+# DB
+MYSQL_DATABASE=datacite
+MYSQL_USER=root
+MYSQL_PASSWORD=
+MYSQL_HOST=mysql
+MYSQL_PORT=3306
+MYSQL_ALLOW_EMPTY_PASSWORD=true
+
+# Logging
+LOG_LEVEL=info
+ADMIN_USERNAME=root
+ADMIN_PASSWORD=
+
 # Authentication
+SESSION_ENCRYPTED_COOKIE_SALT=
+SECRET_KEY_BASE=
 JWT_PUBLIC_KEY=
+JWT_TOKEN=
+JWT_TOKEN_EXPIRED=
 JWT_PRIVATE_KEY=
 
-# AWS SQS queue
+# AWS
 AWS_REGION=
 AWS_ACCESS_KEY_ID=
 AWS_SECRET_ACCESS_KEY=
+
+SITE_TITLE=DataCite API
+PASSENGER_MAX_POOL_SIZE=5
+APP_URL=app.stage.datacite.org
+ES_HOST=elasticsearch:9200
+
+# Mailgun
+MAILGUN_API_KEY=
+MG_DOMAIN=mg.datacite.org
+
+# Needed for tests
+MDS_USERNAME=
+MDS_PASSWORD=
+
+CONCURRENCY=25
+INTEGRATION=1 # Set this environment variable to run the integration tests
+REFRESH=true
+
+STAFF_ADMIN_PASSWORD=
+ORGANIZATION_ADMIN_PASSWORD=
+CONSORTIUM_ADMIN_PASSWORD=
+CLIENT_ADMIN_PASSWORD=
+
+# Handle server config
+HANDLE_URL=https://handle.test.datacite.org
+HANDLE_USERNAME=
+HANDLE_PASSWORD=
+
+# Set to the URL for the test handle server
+HS_REST_URL=https://localhost:8000/api/handles/
+# Set to a homed prefix for the test handle server (including the trailing '/')
+HS_PREFIX=9999/
+
+# Set to appropriate credentials for a user that can create handles in the
+# given prefix. Currently, the API only supports password ('secret key')
+# authentication.
+HS_USER=1234.TEST/ADMIN
+HS_SECKEY=password
+
+# Set to 0 if the test handle server has a self-signed or otherwise invalid SSL
+# certificate
+HS_SSL_VERIFY=0