[RFC] Bump minimum required go version to 1.20 in documentation as required by quic-go

[trashpile-shenanigans]

As of now, compiling in any golang versions older than 1.20 yields the following error:

# github.com/quic-go/quic-go/internal/qtls
../go/pkg/mod/github.com/quic-go/quic-go@v0.40.1/internal/qtls/go_oldversion.go:5:13: cannot use "The version of quic-go you're using can't be built using outdated Go versions. For more details, please see https://github.com/quic-go/quic-go/wiki/quic-go-and-Go-versions." (untyped string constant "The version of quic-go you're using can't be built using outdated Go...) as int value in variable declaration
note: module requires Go 1.20