Update Manifest.cs description of "OpenID Authorization Server" feature

According to this discussion OrchardCMS#15381 (comment) I have added a "Note" in the description of "OpenID Authorization Server" feature. I'm not sure if it's the right place to add a note, but it's the only place available.

src/OrchardCore.Modules/OrchardCore.OpenId/Manifest.cs

@@ -42,7 +42,7 @@
     Id = OpenIdConstants.Features.Server,
     Name = "OpenID Authorization Server",
     Category = "OpenID Connect",
-    Description = "Enables authentication of external applications using the OpenID Connect/OAuth 2.0 standards.",
+    Description = "Enables authentication of external applications using the OpenID Connect/OAuth 2.0 standards. Note: to call the ApiController endpoints of this OrchardCore, you must also enable the 'OpenID Token Validation' feature to perform an OAuth 2.0 authentication.",
     Dependencies =
     [
         OpenIdConstants.Features.Core,