[README.md] Update Bazel Compatibility Matrix (#1143)

README.md

diff --git a/README.md b/README.md
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+++ b/README.md
@@ -11,7 +11,9 @@
 For more information about release and changelogs please see [Changelog](CHANGELOG.md) or refer to the [Github Releases](https://github.com/bazelbuild/rules_kotlin/releases) page.
 
 # `rules_kotlin` Bazel Compatibility
-- HEAD: `5`, `6`
+- HEAD: `6`, `7`
+- [Release 1.9](https://github.com/bazelbuild/rules_kotlin/releases/tag/v1.9.1): `6`, `7`
+- [Release 1.8](https://github.com/bazelbuild/rules_kotlin/releases/tag/v1.8.1): `5`, `6`
 - [Release 1.7](https://github.com/bazelbuild/rules_kotlin/releases/tag/v1.7.1): `4`, `5`, `6`
 
 # Overview