docs: update vision docs

Author: ericc-ch

README.md

@@ -82,6 +82,7 @@ The following command line options are available for the `start` command:
 | --rate-limit   | Rate limit in seconds between requests       | none    | -r    |
 | --wait         | Wait instead of error when rate limit is hit | false   | -w    |
 | --github-token | Provide GitHub token directly                | none    | -g    |
+| --vision       | Enable vision capabilities                   | false   | none  |
 
 ### Auth Command Options
 
@@ -115,6 +116,9 @@ npx copilot-api@latest start --rate-limit 30 --wait
 # Provide GitHub token directly
 npx copilot-api@latest start --github-token ghp_YOUR_TOKEN_HERE
 
+# Enable vision capabilities
+npx copilot-api@latest start --vision
+
 # Run only the auth flow
 npx copilot-api@latest auth