Add a link to Hub API doc from Reference overview page (#12765)

* Add a link to Hub API doc from Reference index

* Minor update

* Fix a typo

Co-authored-by: Usha Mandya <47779042+usha-mandya@users.noreply.github.com>

reference/index.md

@@ -30,6 +30,7 @@ various APIs, CLIs, and file formats.
 |:------------------------------------------------------|:---------------------------------------------------------------------------------------|
 | [Engine API](/engine/api/)                            | The main API for Docker, provides programmatic access to a daemon                      |
 | [Registry API](/registry/spec/api/)                   | Facilitates distribution of images to the engine                                       |
+| [Docker Hub API](/docker-hub/api/latest/)             | API to interact with Docker Hub                                                        | 
 
 ## Drivers and specifications