docs: remove outdated --channel=beta note (#882)

## Summary
Chrome M144 is now in the stable channel, so the note about requiring
`--channel=beta` and the example configuration using it are outdated.

## Prompt
Remove outdated documentation about --channel=beta since Chrome M144 is
now in stable channel.

## Changes
- Removed `--channel=beta` from the `--autoConnect` example
configuration
- Removed the note: "Note: you have to specify `--channel=beta` until
Chrome M144 has reached the stable channel."

## Test plan
- [x] Verified the documentation now reflects the current stable Chrome
version

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Author: vibecodingengine

README.md

@@ -563,15 +563,12 @@ The following code snippet is an example configuration for gemini-cli:
   "mcpServers": {
     "chrome-devtools": {
       "command": "npx",
-      "args": ["chrome-devtools-mcp@latest", "--autoConnect", "--channel=beta"]
+      "args": ["chrome-devtools-mcp@latest", "--autoConnect"]
     }
   }
 }
 ```
 
-Note: you have to specify `--channel=beta` until Chrome M144 has reached the
-stable channel.
-
 **Step 3:** Test your setup
 
 Make sure your browser is running. Open gemini-cli and run the following prompt: