Fix some missing doc links.

Fix some missing doc links.

Replace "=for openssl foreign manuals" with simpler syntax, it looks
like the "=for openssl ifdef" construct.
Fix some broken L<> links; add some missing foreign references and fixed
some typo's.
The WARNINGS in dhparam referred to non-existant commands so reword it.

Fixes #10109

Reviewed-by: Richard Levitte <levitte@openssl.org>
Reviewed-by: Tomas Mraz <tmraz@fedoraproject.org>
(Merged from https://github.com/openssl/openssl/pull/10256)