Fix typos and errors in Ed25519.pod documentation

CLA: trivial
Reviewed-by: NTim Hudson <tjh@openssl.org>
Reviewed-by: NMatthias St. Pierre <Matthias.St.Pierre@ncp-e.com>
(Merged from https://github.com/openssl/openssl/pull/7005)

doc/man7/Ed25519.pod

@@ -13,18 +13,18 @@ one-shot digest sign and digest verify using PureEdDSA and B<Ed25519> or B<Ed448
 (see RFC8032). It has associated private and public key formats compatible with
 draft-ietf-curdle-pkix-04.
 
-No additional parameters can be set during key generation one-shot signing or
-verification. In particular, because PureEdDSA is used, when signing or
-verifying a digest must B<NOT> be specified.
+No additional parameters can be set during key generation, one-shot signing or
+verification. In particular, because PureEdDSA is used, a digest must B<NOT> be
+specified when signing or verifying.
 
 =head1 NOTES
 
 The PureEdDSA algorithm does not support the streaming mechanism
 of other signature algorithms using, for example, EVP_DigestUpdate().
 The message to sign or verify must be passed using the one-shot
-EVP_DigestSign() asn EVP_DigestVerify() functions.
+EVP_DigestSign() and EVP_DigestVerify() functions.
 
-When calling EVP_DigestSignInit() or EVP_DigestSignUpdate() the
+When calling EVP_DigestSignInit() or EVP_DigestVerifyInit(), the
 digest parameter B<MUST> be set to B<NULL>.
 
 Applications wishing to sign certificates (or other structures such as