[Update] Update 'readme_first.txt'.

locales/readme_first.txt

@@ -1 +1,13 @@
-Thank you for considering translating VRCT's UI. However, please refrain from making any changes at this time. I am currently organizing the files, including reordering, adding, and removing elements, and some parts may change frequently until the UI becomes stable. (Note: This message was updated in February 2025.)
+Thank you for considering contributing to VRCT's UI translations.
+If you want to edit a language:
+- If it already exists: edit the corresponding [xx].yml file.
+- If it doesn’t exist: please open a GitHub issue or contact us through another channel. (If you know how to add a new language yourself, feel free to do so! Sorry for the complicated structure...)
+
+Languages currently supported:
+- en: English
+- ja: 日本語
+- ko: 한국어
+- zh-Hant: 繁體中文
+- zh-Hans: 简体中文
+
+Last updated: 2025/09