docs(readme): make English the default README

README.md carried the Chinese version while README.en.md held the English one,
so the GitHub landing page opened in Chinese. Swap them: README.md is now
English and the Chinese version lives in README.zh-CN.md, with both language
switchers pointing at the new paths.

Author: NanmiCoder

.github/workflows/pr-triage.yml

@@ -59,7 +59,7 @@ jobs:
               'src/tools/',
               'src/utils/',
             ]
-            const docsExact = new Set(['README.md', 'README.en.md', 'package.json', 'package-lock.json', '.github/workflows/deploy-docs.yml'])
+            const docsExact = new Set(['README.md', 'README.zh-CN.md', 'package.json', 'package-lock.json', '.github/workflows/deploy-docs.yml'])
             const releaseExact = new Set([
               '.github/workflows/pr-quality.yml',
               '.github/workflows/pr-triage.yml',