docs(badges): tweak badge to use new preview/stable language (#1314) (#140)

Author: gcf-owl-bot[bot]

.github/.OwlBot.lock.yaml

@@ -1,3 +1,3 @@
 docker:
  image: gcr.io/cloud-devrel-public-resources/owlbot-nodejs:latest
- digest: sha256:5ed10ba99cd1ea8c3a0f29b4c53e8a2723a101952705baed6b61783111c64c1c
+ digest: sha256:f092066de33d4a2a13ab13c8fa9dcb4f6b96fa1fb7d391bf19cd0c4921d997c0

README.md

@@ -4,9 +4,8 @@
 
 # [Transcoder API: Node.js Client](https://github.com/googleapis/nodejs-video-transcoder)
 
-
+[![release level](https://img.shields.io/badge/release%20level-stable-brightgreen.svg?style=flat)](https://cloud.google.com/terms/launch-stages)
 [![npm version](https://img.shields.io/npm/v/@google-cloud/video-transcoder.svg)](https://www.npmjs.org/package/@google-cloud/video-transcoder)
-[![codecov](https://img.shields.io/codecov/c/github/googleapis/nodejs-video-transcoder/main.svg?style=flat)](https://codecov.io/gh/googleapis/nodejs-video-transcoder)