feat: update info on listing Slack channels

Author: connorlindsey

content/integrations/chat/slack/sending-a-message-to-channels.mdx

@@ -185,6 +185,8 @@ Remember to consider which roles in your application can access the `SlackAuthBu
 
 This combobox contains the list of channels in the connected Slack workspace. You users will use this combobox to search and select a channel (or more than one channel) to be notified when an event in your application occurs, for example a comment on a video. They can also use this combobox to deselect a connected channel.
 
+To comply with Slack's privacy requirements, this combobox will only display channels the given user has access to. To return private channels, you must resolve the user's email address to their Slack ID. Learn more about [resolving a user's Slack ID](/integrations/chat/slack/sending-a-direct-message#resolving-a-users-slack-id). If the Slack user ID can not be resolved, this combobox will only display public channels.
+
 The combobox automatically shows which channels are already connected, and gives users an easy way to remove them as well.
 
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