Clarify status of the release-1.6 branch

需求 / Requirement

Currently, the main branch is undergoing active development.

The 1.6 branch is too outdated; continuing to maintain it serves little practical purpose and would take time and effort away from maintaining the main branch.

建议实现 / Suggested implements

1. Archive the release-1.6 branch and no longer accept any changes.
2. Notify users through various channels that version 1.6 is no longer suitable for production use and that they should download the 2.0.0 nightly build directly; alternatively, release a first beta version of 2.0 as soon as possible.

备注 / Addition details

No response

Clash Nyanpasu 版本号 / Clash Nyanpasu

N/A

是否为 Pre-release / Is pre-release version

N/A

自查步骤 / Verify steps

• 如果您有足够的时间和能力，并愿意为此提交 PR，请勾上此复选框 / Pull request is welcome. Check this if you want to start a pull request
• 您已仔细查看并知情 Q&A 中的内容 / You have checked Q&A carefully
• 您已搜索过 Issue Tracker，没有找到类似内容 / I have searched on Issue Tracker, No duplicate or related open issue has been found
• 您确保这个 Issue 只提及一个功能。如果您有多个功能请求，烦请发起多个 Issue / Ensure there is only one feature request in this issue. Please make multiply issue for multiply feature request
• 您确保已使用最新 Pre-release 版本测试，并且该功能在最新 Pre-release 版本中并未实现 / This feature have not implemented in latest Pre-release version