Move table cell requirement docs to docs-ui

Move the cell wrapper requirement documentation from the package
README to the docs-ui table component page where it belongs.

Signed-off-by: Patrik Oldsberg <poldsberg@gmail.com>
Made-with: Cursor

packages/ui/README.md

@@ -17,34 +17,6 @@ yarn add @backstage/ui
 - [Backstage Readme](https://github.com/backstage/backstage/blob/master/README.md)
 - [Backstage Documentation](https://backstage.io/docs)
 
-## Table Cell Requirement
-
-When using the `Table` component, every cell rendered via `ColumnConfig.cell` (or
-inside a custom `RowRenderFn`) **must** return a cell component as the top-level
-element. The available cell components are:
-
-- **`CellText`** — displays a title with optional description and icon.
-- **`CellProfile`** — displays an avatar with a name and optional description.
-- **`Cell`** — a generic wrapper for fully custom cell content.
-
-Returning bare text, React fragments, or other elements without wrapping them in
-one of these cell components will break the table layout.
-
-```tsx
-// ✅ Correct — CellText is the top-level element
-cell: item => <CellText title={item.name} />;
-
-// ✅ Correct — Cell wraps custom content
-cell: item => (
-  <Cell>
-    <MyCustomContent value={item.name} />
-  </Cell>
-);
-
-// ❌ Wrong — bare text without a cell wrapper
-cell: item => <span>{item.name}</span>;
-```
-
 ## Writing Changesets for Components
 
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