master docs require updates

[uboness]

• X-Pack installation and setting up page is incorrect
• Both the encryption phrase and SSL are currently required to be configured as part of the installation process. The getting started guide doesn't mention it at all (it's only mentioned in Using Kibana in Production)

[palecur]

PR #7220 is up to bring the X-Pack setting information current. Getting Started will add a section on install-time configuration in a separate PR.

[stacey-gammon]

cc @elastic/kibana-security - want to just double check our current docs are accurate with this, and see if we can close it?

[kobelb]

Yup, we can close it. Thanks Stacey!