Update documenation of PSA_ALG_RSA_PSS

Signed-off-by: Tuvshinzaya Erdenekhuu <tuvshinzaya.erdenekhuu@arm.com>
diff --git a/include/psa/crypto_values.h b/include/psa/crypto_values.h
index 8e61f2f..a4b4927 100644
--- a/include/psa/crypto_values.h
+++ b/include/psa/crypto_values.h
@@ -1330,9 +1330,11 @@
  * This is the signature scheme defined by RFC 8017
  * (PKCS#1: RSA Cryptography Specifications) under the name
  * RSASSA-PSS, with the message generation function MGF1, and with
- * a salt length equal to the length of the hash. The specified
- * hash algorithm is used to hash the input message, to create the
- * salted hash, and for the mask generation.
+ * a salt length equal to the length of the hash, or the largest
+ * possible salt length for the algorithm and key size if that is
+ * smaller than the hash length. The specified hash algorithm is
+ * used to hash the input message, to create the salted hash, and
+ * for the mask generation.
  *
  * \param hash_alg      A hash algorithm (\c PSA_ALG_XXX value such that
  *                      #PSA_ALG_IS_HASH(\p hash_alg) is true).