add description to "Default channel for Slack notifications" UI dropdown (#2051)

# What this PR does
<img width="1005" alt="Screenshot 2023-05-30 at 07 53 20"
src="https://github.com/grafana/oncall/assets/9406895/a3533104-5773-4ce4-b717-74feeca1f0f0">

## Checklist

- [ ] Unit, integration, and e2e (if applicable) tests updated (N/A)
- [ ] Documentation added (or `pr:no public docs` PR label added if not
required) (N/A)
- [x] `CHANGELOG.md` updated (or `pr:no changelog` PR label added if not
required)

CHANGELOG.md

@@ -21,6 +21,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Helm chart: configuration of `uwsgi` using environment variables by @alexintech ([#2045](https://github.com/grafana/oncall/pull/2045))
 - Much expanded/improved docs for mobile app ([2026](https://github.com/grafana/oncall/pull/2026>))
 - Enable by-day selection when defining monthly and hourly rotations ([2037](https://github.com/grafana/oncall/pull/2037))
+- Add description to "Default channel for Slack notifications" UI dropdown by @joeyorlando ([2051](https://github.com/grafana/oncall/pull/2051))
 
 ### Fixed
 

grafana-plugin/src/pages/settings/tabs/ChatOps/tabs/SlackSettings/SlackSettings.tsx

@@ -109,7 +109,10 @@ class SlackSettings extends Component<SlackProps, SlackState> {
                   <Text>{store.teamStore.currentTeam.slack_team_identity?.cached_name}</Text>
                 </div>
               </Field>
-              <Field label="Default channel for Slack notifications">
+              <Field
+                label="Default channel for Slack notifications"
+                description="The selected channel will be used as a fallback in the event that a schedule or integration does not have a configured channel"
+              >
                 <WithPermissionControlTooltip userAction={UserActions.ChatOpsUpdateSettings}>
                   <GSelect
                     showSearch