Incomplete documentation on optional parameters with deep linking and path

Current Behavior

According to tutorials and documentation I managed to gather online, this piece of code should allow for an optional parameter param2, but it seems that it doesn't work and the path is never matched.

 ex: {
        screen: Screen,
      },
    path: "ex/:param1(/:param2)",
  },```

### Expected Behavior

I hoped here that different paths would be matched like:
- app://ex/p1
- app://ex/p1/p2

Both paths should have been matched according to my understanding of the `path` keyword (almost absent from the documentation, hence the issue).

### Your Environment

| software         | version
| ---------------- | -------
| react-navigation | 4.0.10
| react-native     | 0.61.3
| node             | n/a
| npm or yarn      | n/a

issue に記載されている deep-linking のドキュメントと path 設定の例から始めます。react-navigation 4.0.10 でオプションパラメータがどのようにドキュメント化されているかを確認し、ex/p1 と ex/p1/p2 のパスを検証します。ドキュメントでサポートされている構文と期待されるマッチング動作が明確に説明されていれば完了です。