Update the cipher(1) documentation to

explicitly state that the RSA cipher
string means the same a kRSA.

Reviewed-by: Andy Polyakov <appro@openssl.org>
Reviewed-by: Rich Salz <rsalz@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/2821)
(cherry picked from commit f2bcff43)