doc: badge links

[cwtuan]

trafficstars

Hi, I’ve made an update to the README by replacing the NPM download badge with one that links to npm-compare.com, where users can view the dynamic download trends of parse5.

The second badge already links to the NPM page. The third and forth badge now links to npm-compare.com, where users can explore the download trends. This gives users a better perspective on the package’s growth and popularity, instead of simply repeating the link to the NPM package page.

As a maintainer of npm-compare.com, I’m happy to assist with any additional features or insights from our site if needed. Thanks for considering my suggestion!