Remove formatter recommendation section from guide

[koaning]

Removed the section on adding a formatter to the marimo repo. It's better if folks make their own viewers for their own objects.

[vercel]

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Project	Deployment	Actions	Updated (UTC)
marimo-docs	Ready	Preview, Comment	May 1, 2026 4:54pm

[cubic-dev-ai]

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Architecture diagram

sequenceDiagram
    participant UI as marimo UI (Client)
    participant Kernel as marimo Kernel (Server)
    participant Object as User-Defined Object
    participant Internal as marimo Core Formatters

    Note over Object, Internal: Current State: Rendering Flow

    UI->>Kernel: Request cell execution
    Kernel->>Kernel: Evaluate Python code

    Note over Kernel, Object: Protocol Discovery (Preferred Path)
    
    alt Check marimo specific display
        Kernel->>Object: call _display_()
    else Check IPython compatibility
        Kernel->>Object: call _repr_mimebundle_() or _repr_html_()
    else Check marimo mime protocol
        Kernel->>Object: call _mime_()
    end

    Object-->>Kernel: Return rich media / HTML

    opt If no protocols implemented (Legacy/Built-in Path)
        Kernel->>Internal: Lookup type in marimo/_output/formatters
        Internal-->>Kernel: Return formatted output
        Note right of Internal: CHANGED: Contributions to this<br/>directory are now discouraged.
    end

    Kernel-->>UI: Send MIME data for rendering
    UI->>UI: Render output in notebook

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[Copilot]

Pull request overview

Removes documentation guidance that suggests contributing new object formatters directly to the marimo repository, aligning the guide with the stated preference that library authors/users create their own viewers/renderers.

Changes:

• Deleted the “Option 4: Add a formatter to the marimo repo” section from the integration guide.