Add Manager Dashboard guide to Planet manual (fixes #3678)

[Saby-Bishops]

Please verify the following:

• This issue is related to the Virtual Interns First Steps document or Planet User Manual.
• You have searched for relevant keywords in recent open and closed issues to avoid duplicates.

URL to the MDwiki page containing the problem

https://open-learning-exchange.github.io/#!pages/manual/planet/overview.md

Problem

The Planet manual (overview.md) lacks guidance for new admins on how to get started with the Manager dashboard after installation. New administrators need clear instructions on initial setup and dashboard navigation.

Screenshots (when necessary)

Proposed solution(s)

Add a "Getting Started for Admins" section just above the "Become Member" section that includes:
Default login credentials
Overview of Manager Settings features
Guidance on initial setup steps (without password change instruction, as admins can set any password)
Brief introduction to key management functions
This would help new administrators understand the Manager dashboard functionality and improve the onboarding experience.