message: Add note that x-logo SHOULD use absolute URLs
  Have seen a number of definitions designed for use with ReDoc using a relative logo URL. This 'breaks' when someone else (e.g. APIs.guru hosts the API definition).
diff: @@ -93,7 +93,7 @@ The information about API logo
  ###### Fixed fields
  | Field Name | Type | Description |
  | :-------------- | :------: | :---------- |
  -| url | string | The URL pointing to the spec logo. MUST be in the format of a URL
  +| url | string | The URL pointing to the spec logo. MUST be in the format of a URL. It SHOULD be an absolute URL so your API definition is usable from any location
  | backgroundColor | string | background color to be used. MUST be RGB color in [hexadecimal format] (https://en.wikipedia.org/wiki/Web_colors#Hex_triplet)
  