Updated README.md to allow Bootstrap 5 problem

[bastien70]

See #502

I added a Troubleshooting section and the fix for Bootstrap 5 problem

[dunglas]

Thanks!

[arderyp]

Thanks for merging this. You might consider adding another approach:

// call this after crawling to a page if you'd rather not override Bootstrap's default scrolling behavior
$client->executeScript('document.documentElement.style.scrollBehavior = "auto";');