Inidicate latest version in README.md

PiperOrigin-RevId: 511718542
Change-Id: I69628222ba23f1e7f18f57509d899ff9797ca69a

Author: morambro

README.md

@@ -21,6 +21,8 @@ This is an extension to the
 [Tink Java](https://github.com/tink-crypto/tink-java) library that provides
 support for Google Cloud KMS.
 
+The latest version is 1.8.0.
+
 The official documentation is available at https://developers.google.com/tink.
 
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