add a note vault.sh require the same password both keystore and key

When we follow the section "4.2.1.1" and generate the key in the keystore,
some one will set the key password different from keystore password.

However, this will lead the following exception:

WFLYSEC0056: Initializing Vault
MM DD, YYYY 9:50:16 PM org.picketbox.plugins.vault.PicketBoxSecurityVault getAdminKey

INFO: PBOX00371: Security Vault does not contain SecretKey entry under alias ()

To avoid this exception, we need to specify the same password both the keystore and the key in the step creating a keystore.
I looked for any explanation of this behavior, but there is no description for this important fact.

So please add the note to explain the behavior and need to specify the same password in this section.