Correct user add command

Replace outdated command, and remove password from command line, as the
instructions below ("Input the ...") already assume an interactive process,
similar to the master-key prompt above.

Signed-off-by: Georg Pfuetzenreuter <[email protected]>

Author: tacerus

developers.md

@@ -293,10 +293,10 @@ You have to choose a password for the master key and it must be at least 8 chara
 then create vault
 
 ``` sh
-pgmoneta-admin -f pgmoneta_users.conf -U repl -P secretpassword add-user
+pgmoneta-admin -f pgmoneta_users.conf -U repl user add
 ``` 
 
-Input the replication user and its password to grant [**pgmoneta**](https://github.com/pgmoneta/pgmoneta) access to the database. Ensure that the information is correct.
+Input the replication password to grant [**pgmoneta**](https://github.com/pgmoneta/pgmoneta) access to the database. Ensure that the information is correct.
 
 Create the `pgmoneta.conf` configuration file to use when running [**pgmoneta**](https://github.com/pgmoneta/pgmoneta).