Update README-ja.md

Author: taiseiue

README-ja.md

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 # Discord OIDC Proxy
 The proxy that enables applications using OpenID Connect (OIDC) authentication to authenticate users through Discord's OAuth2 system.
 
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-|[English](./README.md)|Japanese|
+[English](./README.md) | **Japanese**
 
 Cloudflare Workers + Hono + pnpm