Update index page to explicitly link to docs for the latest release.

index.html

@@ -2,6 +2,6 @@
 
 <p>Try <a href="https://amaranth-lang.org/play/">Amaranth in your browser</a>.</p>
 
-<p>Read <a href="https://amaranth-lang.org/docs/amaranth/latest/">the latest version of the documentation available</a>.</p>
+<p>Read <a href="https://amaranth-lang.org/docs/amaranth/v0.5.2/">documentation for the latest released version</a>, or <a href="https://amaranth-lang.org/docs/amaranth/latest/">documentation for the in-development, unreleased functionality</a>.</p>
 
 <p>Read <a href="https://amaranth-lang.org/rfcs/">the accepted RFCs</a>.</p>