[docs][rust] Update rust API docs link

The previous link was to an arbitrary (although important) crate.
Instead, point it at rustdoc_index, which is actually intended to serve
as an index page.

Bug: 441377312
Change-Id: Ibf5b4044e9ff54840c41d1d88bcad37ad703671a
Reviewed-on: https://fuchsia-review.googlesource.com/c/api-docs-resources/+/1510136
Reviewed-by: Megan Batty <mgnb@google.com>

public/index.html

diff --git a/public/index.html b/public/index.html
index 1c8b6e7..954ede2 100644
--- a/public/index.html
+++ b/public/index.html
@@ -24,7 +24,7 @@
   <h5><span>Languages</span></h5>
   <ul>
         <li><a href="cpp/index.html">C++ APIs</a></li>
-        <li><a href="rust/fuchsia_component/index.html">Rust APIs</a></li>
+        <li><a href="rust/rustdoc_index/index.html">Rust APIs</a></li>
   </ul>
 </div>