Update get-started-with-ngo.md

[dzhan008]

• Update HelloWorldManager.cs code snippet to fix build errors
• Moved/updated some text for better instruction flow
• Added notes for extra clarity

WARNING: Please make your PR against the develop branch.

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Select the type of change:

• Small Changes - Typos, formatting, slight revisions
• New Content - New features, sections, pages, tutorials
• Site and Tools - Updates, maintenance, and new packages for the site and Docusaurus

Purpose of the Pull Request:

I finished this quickstart guide recently but ran into some issues throughout the tutorial. I wanted to address updates to this page to better help the flow of going through this part of the docs. Here are the details of what I changed:

• Updated the HelloWorldManager.cs example with the following:
  • NetworkManager is now static, as it caused build errors with other static methods and probably should be its own instance anyway
  • Commented references to SubmitNewPosition() since HelloWorldPlayer.cs is not introduced until later in the tutorial, but before building for other steps
• In Test the RPCs section, I removed the build steps and replaced it with setting up Multiplayer Play Mode. You can't see logs through builds unless you enable development builds, and even then only Debug.LogError is displayed
• Updated outdated MPMM links
• Added some new notes for clarity, including one where you don't need to update the NetworkVariable position in HelloWorldPlayer.cs anymore since technically NetworkTransform handles this out of box

As a note, with Unity 6 out some of the general for creating scripts/running builds are slightly different now. I held off on these changes since they were small, but wanted to bring this up for awareness.

Issue Number: N/A

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