feat: promote to 1.0.0 (#586)

Release-As: 1.0.0

.repo-metadata.json

@@ -4,7 +4,7 @@
   "product_documentation": "https://cloud.google.com/resource-manager",
   "client_documentation": "https://googleapis.dev/java/google-cloud-resourcemanager/latest/",
   "issue_tracker": "https://issuetracker.google.com/savedsearches/559757",
-  "release_level": "alpha",
+  "release_level": "ga",
   "language": "java",
   "repo": "googleapis/java-resourcemanager",
   "repo_short": "java-resourcemanager",

README.md

@@ -8,9 +8,6 @@ Java idiomatic client for [Resource Manager API][product-docs].
 - [Product Documentation][product-docs]
 - [Client Library Documentation][javadocs]
 
-> Note: This client is a work-in-progress, and may occasionally
-> make backwards-incompatible changes.
-
 
 ## Quickstart
 
@@ -303,9 +300,6 @@ and on [google-cloud-java][g-c-j].
 This library follows [Semantic Versioning](http://semver.org/).
 
 
-It is currently in major version zero (``0.y.z``), which means that anything may change at any time
-and the public API should not be considered stable.
-
 
 ## Contributing
 
@@ -347,7 +341,7 @@ Java is a registered trademark of Oracle and/or its affiliates.
 [kokoro-badge-link-4]: http://storage.googleapis.com/cloud-devrel-public/java/badges/java-resourcemanager/java8-win.html
 [kokoro-badge-image-5]: http://storage.googleapis.com/cloud-devrel-public/java/badges/java-resourcemanager/java11.svg
 [kokoro-badge-link-5]: http://storage.googleapis.com/cloud-devrel-public/java/badges/java-resourcemanager/java11.html
-[stability-image]: https://img.shields.io/badge/stability-alpha-orange
+[stability-image]: https://img.shields.io/badge/stability-ga-green
 [maven-version-image]: https://img.shields.io/maven-central/v/com.google.cloud/google-cloud-resourcemanager.svg
 [maven-version-link]: https://search.maven.org/search?q=g:com.google.cloud%20AND%20a:google-cloud-resourcemanager&core=gav
 [authentication]: https://github.com/googleapis/google-cloud-java#authentication