Disclaimer in README.md about non-production readiness

Can we add a disclaimer in the README that NSS should not be used with production data? I've found that it's used in production and marketed as a "secure" place to store your data.

There's already following disclaimer in the index.html file:

This is a prototype implementation of a Solid server. It is a fully functional server, but there are no security or stability guarantees.

I think it serves the purpose of a prototype server well. But I think we should copy this disclaimer to the README to make clear expectations.

(And while it would be nice to get it production ready, I suppose there are not enough resources to make it secure in the near future)

將 index.html 中現有的免責聲明與 README.md 進行比較，從 README 的簡介或專案描述開始。完成的標準是 README 明確包含相同的原型、安全性與穩定性警告；不涉及程式碼變更。