openssl_csr: Improved documentation on subject_alt_name possible values

lib/ansible/modules/crypto/openssl_csr.py

@@ -108,6 +108,8 @@ options:
         description:
             - SAN extension to attach to the certificate signing request
             - This can either be a 'comma separated string' or a YAML list.
+            - Values should be prefixed by their options. (ie. email, URI, DNS, RID, IP, dirName, otherName and the ones specific to your CA)
+            - More at U(https://tools.ietf.org/html/rfc5280#section-4.2.1.6)
     subject_alt_name_critical:
         required: false
         aliases: [ 'subjectAltName_critical' ]