Create README.md

Author: ArthurYCQ

README.md

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+# Usage
+
+```
+@State private var text: String = ""
+@FocusState private var isActive: Bool
+
+YYTextFieldWithKeyboard {
+    TextField("", text: $text)
+        .padding(.horizontal, 10)
+        .padding(.vertical, 6)
+        .frame(width: 150)
+        .focused($isActive)
+} keyboard: {
+    CustomNumberKeyboard(text: $text, isActive: $isActive, config: .default)
+}
+```