docs: document clawdbot update

docs/cli/index.md

@@ -14,6 +14,7 @@ This page describes the current CLI behavior. If commands change, update this do
 - `--dev`: isolate state under `~/.clawdbot-dev` and shift default ports.
 - `--profile <name>`: isolate state under `~/.clawdbot-<name>`.
 - `--no-color`: disable ANSI colors.
+- `--update`: shorthand for `clawdbot update` (source installs only).
 - `-V`, `--version`, `-v`: print version and exit.
 
 ## Output styling
@@ -47,6 +48,7 @@ clawdbot [--dev] [--profile <name>] <command>
   onboard
   configure (alias: config)
   doctor
+  update
   providers
     list
     status