chore(release): 8.1.0 stable release notes (#16436)

# Overview

Release notes, meant to be final for 8.1.0 stable.

## Test Plan and Hands on Testing

👀 

## Changelog

Added a line in `app-shell` notes for fixing the bug that shows the
"welcome" screen on robots that are already set up.

## Review requests

🚢 ❓ 

## Risk assessment

none.

Author: ecormany

app-shell/build/release-notes.md

@@ -12,7 +12,11 @@ By installing and using Opentrons software, you agree to the Opentrons End-User
 
 Welcome to the v8.1.0 release of the Opentrons App!
 
-There are no changes to the Opentrons App in v8.1.0, but it is required for updating the robot software to support the latest production version of Flex robots.
+There are no new features in the Opentrons App in v8.1.0, but it is required for updating the robot software to support the latest production version of Flex robots.
+
+### Bug Fixes
+
+- Prevented Flex from showing the first-run screen when powering on a robot that's already set up.
 
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