chore: add type definition

__tests__/index.test.ts

@@ -0,0 +1,26 @@
+import QrcodeDecoder from '../';
+
+describe('QrcodeDecoder', () => {
+  test('use', async () => {
+    const res = await import('../dist');
+
+    expect(res.default).toEqual(QrcodeDecoder);
+  });
+
+  test('new QrcodeDecoder()', async () => {
+    const qr = new QrcodeDecoder();
+
+    expect(qr).toBeDefined();
+    expect(qr.videoConstraints).toEqual({
+      video: {
+        width: { min: 360, ideal: 720, max: 1080 },
+        height: { min: 360, ideal: 720, max: 1080 },
+        facingMode: { exact: 'environment' },
+      },
+      audio: false,
+    });
+    expect(qr.decodeFromImage).toBeDefined();
+    expect(qr.decodeFromCamera).toBeDefined();
+    expect(qr.decodeFromVideo).toBeDefined();
+  });
+});