Suggestion: add Playwright browser install troubleshooting to README

[yangsi7]

The README currently notes that crawling requires playwright and browser dependencies, but it may be helpful to add a short troubleshooting section for a common launch failure. The error is confusing and the crawl command can fail if the Playwright browser revision expected by Clipper is missing from the local Playwright cache.

Example error:

Failed to launch browser.
browserType.launchPersistentContext: Executable doesn't exist at:
~/Library/Caches/ms-playwright/chromium-1140/...

The error may suggest:

npx playwright install

However, when Clipper is installed globally, this can install the browser revision for whatever Playwright version npx resolves to, which may not match the Playwright version bundled with Clipper.

Suggested README addition:

## Troubleshooting
### `clipper crawl` fails with `Failed to launch browser`
If crawling fails because Playwright cannot find a Chromium executable, install the Chromium browser for the Playwright version bundled with Clipper.
For a global npm install, run:
```bash
$(npm root -g)/@philschmid/clipper/node_modules/.bin/playwright install chromium

If system dependencies are also missing, run:

$(npm root -g)/@philschmid/clipper/node_modules/.bin/playwright install --with-deps chromium

Then retry:

clipper crawl -u <url>
This avoids installing a browser revision for a different Playwright version than the one Clipper uses.