Small doc fixes found by the linkchecker

Signed-off-by: Sven Dowideit <SvenDowideit@home.org.au>

docs/spec/auth/index.md

@@ -0,0 +1,14 @@
+<!--[metadata]>
++++
+title = "Docker Regidtry Token Authentication"
+description = "Docker Registry v2 authentication schema"
+keywords = ["registry, on-prem, images, tags, repository, distribution, authentication, advanced"]
+[menu.main]
+parent="smn_registry_ref"
++++
+<![end-metadata]-->
+
+# Docker Registry v2 authentication
+
+See the [Token Authentication Specification](token.md) and
+[Token Authentication Implementation](jwt.md) for more information.