message: Clarify mandoc
diff: @@ -161,7 +161,7 @@ The output has the following format:
  }
  },
  /* List of registries to which this package may be published.
  - This is null if not specified. */
  + Publishing is unrestricted if null, and forbidden if an empty array. */
  "publish": [
  "crates-io"
  ],
  