More early data documentation updates following feedback

Reviewed-by: NRich Salz <rsalz@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/2737)

doc/man1/s_server.pod

@@ -529,11 +529,12 @@ The list should contain most wanted protocols first.
 Protocol names are printable ASCII strings, for example "http/1.1" or
 "spdy/3".
 
-=item B<-max_early_data>
+=item B<-max_early_data arg>
 
 Change the default maximum early data bytes that are specified for new sessions
 and any incoming early data (when used in conjunction with the B<-early_data>
-flag). The default value is approximately 16k.
+flag). The default value is approximately 16k. The argument must be an integer
+greater than or equal to 0.
 
 =item B<-early_data>
 

doc/man3/SSL_read_early.pod → doc/man3/SSL_read_early_data.pod

@@ -42,7 +42,7 @@ Early data has weaker security properties than other data sent over an SSL/TLS
 connection. In particular the data does not have forward secrecy and there are
 no guarantees that the same early data was not replayed across multiple
 connections. For this reason extreme care should be exercised when using early
-data.
+data. For specific details, consult the TLS 1.3 specification.
 
 When a server receives early data it may opt to immediately respond by sending
 application data back to the client. Data sent by the server at this stage is