docs(cli): document account switching

Author: c8dhjp4tyv-bit

README.md

@@ -28,6 +28,12 @@ freebuff
 
 Then describe what you want. Freebuff finds the relevant files, makes changes, and runs the checks that matter for your project.
 
+### Switch accounts
+
+To change the account used by the CLI, enter `/logout` (or `/signout`) in an
+active session. After logging out, press Enter on the login screen, or run
+`freebuff login` from your shell to start the browser login flow again.
+
 ## Models
 
 Freebuff includes a curated model catalog. The regular picker currently offers: