Please update the "Certificate Compatibility" page to include information about the new ISRG roots

we will update that page soon

@jsha it would be helpful if we have the compatibility list of ISRG Root so that we could help our customers with this transition.

@Devarajan related issue:

Thanks to @felixf's hard work Pebble v2.1.0 has implemented RFC 8555 Section 7.4.2's description of rel="alternative" links.