message: Add clarification that Location spec is required
diff: @@ -1266,6 +1266,9 @@ shape, this kind has the following structure.
  Exactly equal to `backstage.io/v1alpha1` and `Location`, respectively.
  +### `spec` [required]
  +The `spec` field is required. The miniaml spec should be an empty object.
  +
  ### `spec.type` [optional]
  The single location type, that's common to the targets specified in the spec. If
  