docs(desktop): an agent can be added from the app later, under its real menu name

The desktop README's Known limits still said an agent is added by hand after the install, and the wiki gave the menu item a shorter name than the one the app shows.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

packages/desktop/README.md

@@ -330,9 +330,10 @@ and the Dock icon bounces.
 - **Who can reach it stops at the local network.** Tailscale needs its own
   login and setup, which the installer does at a terminal. Choose *Install in
   Terminal instead*, or run `install.sh tailscale` later.
-- **The agent is chosen during the install.** With Codeman already installed,
-  or after *Skip for now*, an agent is added by hand: its commands are in the
-  installer's closing notes and in [Installing an agent CLI](../../docs/wiki/Installation.md#installing-an-agent-cli).
+- **An agent is chosen during the install, or added later.** With Codeman
+  already installed, or after *Skip for now*, *Add a coding agent* on the This
+  Mac tab (*Add a Coding Agent to This Mac…* in the app menu) installs one. The
+  commands are also in [Installing an agent CLI](../../docs/wiki/Installation.md#installing-an-agent-cli).
 - **An agent only your interactive profile finds counts as missing.** The app
   reads the login shell's environment, without `.zshrc`, so a CLI on an nvm
   PATH set up there is offered again as if it were not installed. Installing