Commented permissions required by our Slack bot. (#2668)

To reduce confusion, added comments to slack bot permissions.

docs/sources/notify/slack/index.md

@@ -40,6 +40,56 @@ For Open Source Grafana OnCall Slack installation guidance, refer to
 1. Provide your Slack workspace URL and sign with your Slack credentials.
 1. Click **Allow** to give Grafana OnCall permission to access your Slack workspace.
 
+## Why does OnCall Slack App require so many permissions?
+OnCall has an advanced Slack App with dozens of features making it even possible for users to be on-call and work with 
+alerts completely inside Slack. The drawback is that our Slack bot requires a lot of permissions and
+some of those permissions may sound suspicious, so we commented on them to give you more context.
+#### Content and info about you
+The bot is using those permissions to receive Slack handles and avatars. 
+Those permissions are supporting account matching between Grafana and Slack. 
+- **View information about your identity**
+- **View profile details about people in your workspace**
+#### Content and info about channels & conversations
+- **View basic information about public channels in your workspace** 
+— this permission is supporting channel selectors in the integration settings so the user could choose where to 
+send Alert Groups.
+- **View messages and other content in public channels, private channels, direct messages, and group direct messages 
+that Grafana OnCall has been added to** — this permission is supporting a feature of adding messages to the resolution 
+notes in the Alert Group's Slack thread.
+- **View basic information about private channels that Grafana OnCall has been added to** — this permission allows to 
+add a slack bot to the private channel and make it selectable in the list of channels. 
+So users will be able to route Alert Groups to the private channels.
+- **View basic information about direct messages that Grafana OnCall has been added to**
+#### Content and info about your workspace
+This set of permissions is supporting the ability of Grafana OnCall to match users with Grafana users.
+- **View people in your workspace**
+- **View email addresses of people in your workspace**
+- **View the name, email domain, and icon for workspaces Grafana OnCall is connected to**
+- **View user groups in your workspace**
+- **View profile details about people in your workspace**
+#### Perform actions as you
+- **Send messages on your behalf** — this permission may sound suspicious, but it's actually a general ability 
+to send messages as the bot: https://api.slack.com/scopes/chat:write Grafana OnCall will not impersonate or post 
+using your handle to slack. It will always post as the bot.
+#### Perform actions in channels & conversations
+- **View messages that directly mention @grafana_oncall in conversations that the app is in**
+- **Join public channels in your workspace**
+- **Send messages as @grafana_oncall**
+- **Send messages as @grafana_oncall with a customized username and avatar**
+- **Send messages to channels @grafana_oncall isn't a member of** — users configure channels to publish 
+Alert Groups in the OnCall's UI, but the bot is usually not a member of those channels.
+- **Upload, edit, and delete files as Grafana OnCall** — the bot is using this permission: 
+https://api.slack.com/scopes/files:write to be able to send files to the channel. 
+The bot will not delete or read files sent by other users.
+- **Start direct messages with people**
+- **Add and edit emoji reactions**
+#### Perform actions in your workspace
+- **Add shortcuts and/or slash commands that people can use** — the permission is used to add /escalate and /oncall 
+(deprecated) slack commands.
+- **Create and manage user groups** — the permission is used to automatically update user groups linked to on-call
+schedules. It will add users once their on-call shift starts and remove them once the on-call shift ends.
+- **Set presence for Grafana OnCall** 
+
 ## Post-install configuration for Slack integration
 
 Configure the following additional settings to ensure Grafana OnCall alerts are routed to the intended Slack channels