Auto merge of #11538 - ehuss:fix-docs-links, r=weihanglo

Fix some doc links

This fixes some links that were broken during the reorganization in #11480.

Author: bors

src/doc/src/reference/registries.md

@@ -104,6 +104,7 @@ token = "854DvwSlUwEHtIo3kWy6x7UCPKHfzCmy"
 [`cargo package`]: ../commands/cargo-package.md
 [`cargo login`]: ../commands/cargo-login.md
 [config]: config.md
+[crates.io]: https://crates.io/
 
 <script>
 (function() {

src/doc/src/reference/registry-index.md

@@ -203,3 +203,5 @@ The JSON objects should not be modified after they are added except for the
 `yanked` field whose value may change at any time.
 
 [`cargo publish`]: ../commands/cargo-publish.md
+[alphanumeric]: ../../std/primitive.char.html#method.is_alphanumeric
+[crates.io]: https://crates.io/