Link to release (non-snapshot) API documentation from README and wiki

[mernst]

At https://guava.dev/releases/snapshot-jre/api/docs/ I typed "Parameter" into the search box at the upper right. See screenshot.

I clicked on the first match, which took me to
https://guava.dev/releases/snapshot-jre/api/docs/undefined/com/google/common/reflect/Parameter.html
which gave me a 404 error.

In addition to fixing this problem, I think it would be helpful to users to have a link to the stable (non-snapshot) API documentation, from both the README shown at https://github.com/google/guava and from https://github.com/google/guava/wiki .

[cpovirk]

Thanks. The search issue is #5457, which maybe we should fix by building Javadoc with a newer JDK.

Our approach for Javadoc has been to link to the Javadoc for a release from its page, e.g., https://github.com/google/guava/releases/tag/v30.1.1. Maybe @cgdecker has thoughts on whether to also include that on the landing page -- or maybe to link from the landing page's "Snapshots and Documentation" section to the Releases page?