docs: add QQ community group to README (EN + ZH)

[ranxianglei]

Add a QQ community group (1056132097) to the README in both English and Chinese.

One shared group covers all three projects: billion-context, billion-context-pi, opencode-acp.

• README.md: new ## Community section before ## License
• README.zh-CN.md: new ## 社区 section before ## 许可证

Docs-only; no version bump.

[github-actions]

📦 Built Package Artifact

Branch: 2026-09-11_readme-qq-group (2f80a4c)

Option A — Install from npm PR tag (recommended)

npm install -g billion-context@pr-704

Each push to this PR publishes a new version under the pr-704 npm tag.

Option B — Download artifact

1. Download the artifact from the Actions run
2. Extract the tarball and install:

tar xzf billion-context-pr704.tgz
npm install -g package

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This comment is automatically updated on each push.

[ranxianglei]

🤖 Powered by ework · qwen3.8-27b

[bot] 🏷 Received — adding QQ group 1056132097 as a ## Community / ## 社区 section before License/许可证 in both READMEs. Docs-only, no version bump. Opening a PR shortly.

[ranxianglei]

🤖 Powered by ework · qwen3.8-27b

[bot] 🏷 Done — PR opened: #705

What's in it:

• README.md: new ## Community section before ## License — QQ group 1056132097, one shared group for all three projects, each linked (billion-context, billion-context-pi, opencode-acp)
• README.zh-CN.md: matching ## 社区 section before ## 许可证 (Chinese wording, same group number and links)

Docs-only; no version bump, no code touched. Branch is rebased onto latest master. Ready for review/merge.