Some content has been moved out into the general libraries introduction.
Reformat and fill in some gaps with what remains.
Reviewed-by: Hugo Landau <hlandau@openssl.org>
Reviewed-by: Tim Hudson <tjh@openssl.org>
Reviewed-by: Matthias St. Pierre <Matthias.St.Pierre@ncp-e.com>
Reviewed-by: Anton Arapov <anton@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/21560)
