Add guild feature

Author: Lulalaby

discord/guild.py

@@ -223,6 +223,7 @@ class Guild(Hashable):
         - ``PREVIEW_ENABLED``: Guild can be viewed before being accepted via Membership Screening.
         - ``PRIVATE_THREADS``: Guild has access to create private threads.
         - ``ROLE_ICONS``: Guild can set an image or emoji as a role icon.
+        - ``ROLE_SUBSCRIPTIONS_AVAILABLE_FOR_PURCHASE``: Role subscriptions are available for purchasing.
         - ``ROLE_SUBSCRIPTIONS_ENABLED``: Guild is able to view and manage role subscriptions.
         - ``SEVEN_DAY_THREAD_ARCHIVE``: Guild has access to the seven day archive time for threads.
         - ``TEXT_IN_VOICE_ENABLED``: Guild has a chat button inside voice channels that opens a dedicated text channel in a sidebar similar to thread view.