We also add reference for ALPN ids
Reviewed-by: NHugo Landau <hlandau@openssl.org>
Reviewed-by: NTomas Mraz <tomas@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/22505)

We move some of the "why QUIC" content into the guide and just provide a
summary in README-QUIC.md.

We also clarify how to use s_client with QUIC.
Reviewed-by: NHugo Landau <hlandau@openssl.org>
Reviewed-by: NTomas Mraz <tomas@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/22505)