Add directory for Kubernetes Upstream Training in Japan at CNDW2025

Add README.md for now.

Author: shu-mutou

japan/cndw-2025/README.md

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+# Kubernetes Upstream Training in Japan at [CNDW2025](https://event.cloudnativedays.jp/cndw2025/)
+
+Welcome to Kubernetes Upstream Training!!
+
+This is the location of [Cloud Native Community Japan](https://community.cncf.io/cloud-native-community-japan/) SIG Kubernetes Upstream Training Japan (Japanese Only) activities.
+
+ここは、[CNCJ](https://community.cncf.io/cloud-native-community-japan/)のサブチャプターであるKubernetes Upstream Training Japan が2025/11/14に開催するトレーニングのためのページです。
+
+[イベント概要と参加登録はこちら](https://community.cncf.io/e/mpjcgm/)
+
+## 資料 (Documents)
+
+* [参加者の皆様への宿題 Attendee prerequisites (in preparation)](../assets/attendee-prerequisites.md)
+* [スライド Slides](../assets/slide.pdf)
+* [Kubernetes contributors guide](https://github.com/kubernetes/community/tree/master/contributors/guide)
+
+## 講師（Facilitators）
+
+| Icon | Name | Affiliation | Slack | Focus on, Role.. |
+| -----| ---- | ----------- | ----- | ---------------- |
+| TBD | TBD | TBD | TBD | TBD |
+
+## We got new contributors!!
+
+TBD