Update ViewportAdapter Docs To Note Initializing In Game1 Causes Null Excecption Later

[AristurtleDev]

Description

If a viewport adapter is initialized in the game1 constructor, the GraphicsDevice instance that it uses isn't instantiated yet, so it receives a null instance. The documentation already shows it correctly being done in the Game.Initialize method, but a note should be added to explain that's where to do it and why not to do it in the Game.ctor

Steps to Reproduce

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Expected Behavior

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Actual Behavior

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Configuration

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Other Information

Discovered from discord conversation: https://discord.com/channels/465739026700173312/509740842936696832/1482783806292361387