Document usage of environment variables in the runtime manifest

[shazron]

1. Set your env var in your .env https://developer.adobe.com/app-builder/docs/guides/appbuilder-configuration/#env
2. Then in your app.config.yaml runtimeManifest you can refer to the env var in your action inputs by prefixing it with $. For example in the screenshot, $LOG_LEVEL . This will be a parameter passed in to your action.

1. Sample runtimeManifest: https://github.com/apache/openwhisk-wskdeploy/blob/master/docs/examples/manifest_hello_world_env_var_parms.yaml
2. How it's accessed in the action: https://github.com/apache/openwhisk-wskdeploy/blob/master/docs/examples/src/hello.js

[aiojbot]

JIRA issue created: https://jira.corp.adobe.com/browse/AIOE-664