docs(node): support "stable"/"preview" release level (#1312) (#101)

Author: gcf-owl-bot[bot]

packages/google-cloud-networkconnectivity/README.md

@@ -124,12 +124,14 @@ This library follows [Semantic Versioning](http://semver.org/).
 
 
 
+
 This library is considered to be in **alpha**. This means it is still a
 work-in-progress and under active development. Any release is subject to
 backwards-incompatible changes at any time.
 
 
 
+
 More Information: [Google Cloud Platform Launch Stages][launch_stages]
 
 [launch_stages]: https://cloud.google.com/terms/launch-stages