Update documentation about dependency ServiceManager

[weierophinney]

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Using the most complete version of the component with SmtpOptions and SmtpTransport a dependency error is reported and in relation to this has already been discussed previously.

problem and solution #62

But the documentation is not good for this use.

I suggest that in these two links be informed about the dependency:

(1) https://docs.zendframework.com/zend-mail/transport/smtp-authentication/#smtp-authentication
(2) https://docs.zendframework.com/zend-mail/transport/smtp-options/

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Originally posted by @eduardobona at zendframework/zend-mail#219

[alexmerlin]

Closing issue due to being inactive for more than 1 year.