Add descriptions to VisibilityLevelsEnum

app/graphql/types/visibility_levels_enum.rb

@@ -3,7 +3,7 @@
 module Types
   class VisibilityLevelsEnum < BaseEnum
     Gitlab::VisibilityLevel.string_options.each do |name, int_value|
-      value name.downcase, value: int_value
+      value name.downcase, value: int_value, description: "#{name.titleize} visibility level."
     end
   end
 end

doc/api/graphql/reference/index.md

@@ -5664,9 +5664,9 @@ Possible states of a user.
 | Value | Description |
 | ----- | ----------- |
-| `internal` |  |
-| `private` |  |
-| `public` |  |
+| `internal` | Internal visibility level. |
+| `private` | Private visibility level. |
+| `public` | Public visibility level. |
 ### VisibilityScopesEnum