ICU-23055 add contacts page from ICU Site

See #3519

Author: markusicu

docs/contacts.md

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+---
+layout: default
+title: Contacts and Mailing Lists
+nav_order: 150
+---
+
+<!--
+© 2025 and later: Unicode, Inc. and others.
+License & terms of use: http://www.unicode.org/copyright.html
+-->
+
+# Contacts and Mailing Lists
+
+ICU uses several mailing lists for discussions, announcements and notifications. The mailing list server provides web-based subscription with several options, list archives, digest mode, etc. Please follow the links to the mailing lists you are interested in.
+
+*Note:* In order to post to the support or design lists you *must subscribe first* — posts by non-members are rejected. You can browse the list archives without subscribing by following the links below, or search the archives.
+
+As a general rule of etiquette, please do not include confidential information or mark your emails as urgent. These are public mailing lists used by many volunteers. The volunteers will try to answer your question as soon as possible.
+
+## Mailing lists
+
+**[[email protected]](https://groups.google.com/a/unicode.org/g/icu-support)**
+
+ICU C/C++/Java usage discussions, support and platform specific issues (e.g. downloading, compiling, linking, packaging, debugging, ICU API usage, ICU data, etc.)
+
+You can also subscribe by sending an email to [email protected]
+
+**[[email protected]](https://groups.google.com/a/unicode.org/g/icu-announce)**
+
+Contains important announcements about the ICU project, such as new releases. **Read-only.**
+
+You can also subscribe by sending an email to [email protected]
+
+**[[email protected]](https://groups.google.com/a/unicode.org/g/icu-design)**
+
+This list is for API proposals and their discussion. *(If you have a problem building ICU, or a question about using ICU, do not use this list — use icu-support instead.)*
+
+You can also subscribe by sending an email to [email protected]
+
+## Bugs & feature requests
+
+You can **report a bug or request a new feature** with the [bug tracking system](https://icu.unicode.org/bugs). (This is not a mailing list, but a web-based bug tracking system). If you have an ICU4C or ICU4J build problem, you will get a faster response from the icu-support mailing list. Please do not use the icu-design mailing list for build issues.
+
+## Obsolete mailing lists
+
+The following mailing lists preserve archived discussions. They are closed for new discussion.
+
+https://groups.google.com/a/unicode.org/g/icu-charsets
+
+An archived list about ICU conversion data and API. (inactive list; active 2001-2003)
+
+https://groups.google.com/a/unicode.org/g/icu-issues
+
+An archived list of pre-issue-tracker ICU issues (inactive list; active 2001-2004)