feat: with nothing to show, the right pane says how to get started

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

README.md

@@ -60,7 +60,8 @@ lazysecrets         # start lazysecrets
 lazysecrets --demo  # test with demo data
 ```
 
-Pick a source on the left, then a vault, then a secret. The keys you'll
+Pick a source on the left, then a vault, then a secret. With nothing
+signed in yet, the right pane says how to get started. The keys you'll
 use most:
 
 | Key | Action |