Add README

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: ivanvorobei

README.md

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+# DiffableKit
+
+Wrapper around `UITableViewDiffableDataSource` and `UICollectionViewDiffableDataSource`. Removes boilerplate — describe sections and rows as models, get animated updates out of the box.
+
+Built-in row types for settings screens. Cell provider, header/footer provider, delegate with actions — all wired up declaratively.
+
+```swift
+class SettingsController: DiffableTableController {
+
+    override func viewDidLoad() {
+        super.viewDidLoad()
+        configureDiffable(
+            sections: [
+                DiffableSection(
+                    id: "general",
+                    header: DiffableTextHeaderFooter(text: "General"),
+                    items: [
+                        DiffableTableRow(text: "Theme", detail: "System", accessoryType: .disclosureIndicator)
+                    ]
+                )
+            ],
+            cellProviders: DiffableTableDataSource.CellProvider.default
+        )
+    }
+}
+```