Move stray POD file into the fold

Reviewed-by: Matthias St. Pierre <Matthias.St.Pierre@ncp-e.com>
(Merged from https://github.com/openssl/openssl/pull/8273)

diff --git a/doc/man3/X509_cmp_time.pod b/doc/crypto/X509_cmp_time.pod
similarity index 100%
rename from doc/man3/X509_cmp_time.pod
rename to doc/crypto/X509_cmp_time.pod