Auto merge of #14228 - yukionfire:patch001, r=arlosi

chore(docs): update index of reference

add missing section in the index page of reference

Author: bors

src/doc/src/reference/index.md

@@ -19,6 +19,11 @@ The reference covers the details of various areas of Cargo.
 * [Source Replacement](source-replacement.md)
 * [External Tools](external-tools.md)
 * [Registries](registries.md)
+    * [Registry Authentication](registry-authentication.md)
+        * [Credential Provider Protocol](credential-provider-protocol.md)
+    * [Running a Registry](running-a-registry.md)
+        * [Registry Index](registry-index.md)   
+        * [Registry Web API](registry-web-api.md) 
 * [Dependency Resolution](resolver.md)
 * [SemVer Compatibility](semver.md)
 * [Future incompat report](future-incompat-report.md)