Clarify Azure Translator resource region requirement (#6363)

Added note about setting the translator resource region to Global to
avoid 401 errors.

## Description

Had a bit of trouble with the lyrics plugin where the translator was not
working. Creating a global resource instead of a regional one fixed the
issue. Added a small note to the documentation so that people won't run
into the same issue in the future.

For a bit more info, you need to specify the region in the request
headers if its a regional resource. This is not required for a global
one.

Author: snejus

docs/plugins/lyrics.rst

@@ -174,6 +174,9 @@ We use Azure to optionally translate your lyrics. To set up the integration,
 follow these steps:
 
 1. `Create a Translator resource`_ on Azure.
+       Make sure the region of the translator resource is set to Global. You
+       will get 401 unauthorized errors if not. The region of the resource group
+       does not matter.
 2. `Obtain its API key`_.
 3. Add the API key to your configuration as ``translate.api_key``.
 4. Configure your target language using the ``translate.to_language`` option.