added Limit order FAQ

Author: HubertHalim

docs/pendle-v2/AppGuide/LimitOrder.md

@@ -62,3 +62,14 @@ hide_table_of_contents: true
 
 
 **Please make sure to keep both the placing limit order browser tab and the Safe Wallet browser tab always open throughout the placing limit order process.**
+
+
+## FAQ
+
+**Why is there a large gap between the AMM spot APY and the best bid in the orderbook, but no arbitrage is happening?**
+
+Arbitrageurs factor in fees from both the AMM and the orderbook when deciding whether to act. A trade is only profitable if the spread between the two exceeds the combined fees of both systems. For example, if the orderbook fee is 0.2% and the AMM fee is 0.15%, arbitrage will only occur when the spread exceeds 0.35%. Below that threshold, the trade would be unprofitable after fees, so no arbitrage takes place.
+
+**Why is only ~90% of my swap routed through the orderbook, even though it offers a better price?**
+
+This is by design. A small portion of every swap is always routed through the AMM as a safety buffer. Orderbook execution can occasionally result in dust amounts — tiny leftovers that are too small to process further. Without the AMM fallback, those dust amounts would either need to be returned to you (requiring an additional swap) or burned. By routing a small slice through the AMM, all funds are guaranteed to be fully utilized, since the AMM provides continuous liquidity at all times.

i18n/cn/docusaurus-plugin-content-docs/current/AppGuide/LimitOrder.md

@@ -18,3 +18,13 @@ hide_table_of_contents: true
 2. 您的订单填充状态将在表中显示，直至其到期日期，之后将显示在**我的订单历史**表中。
 
 
+## 常见问题
+
+**为什么 AMM 现货 APY 与订单簿中最高买价之间存在较大差距，但没有套利发生？**
+
+套利者在决定是否行动时，会将 AMM 和订单簿的手续费都纳入考量。只有当两者之间的价差超过综合手续费时，套利才有利可图。例如，如果订单簿手续费为 0.2%，AMM 手续费为 0.15%，则只有当价差超过 0.35% 时才会发生套利。低于该阈值，扣除手续费后交易将无利可图，因此不会发生套利。
+
+**为什么即使订单簿提供更好的价格，我的兑换中也只有约 90% 通过订单簿路由？**
+
+这是经过特别设计的。每次兑换都有一小部分始终通过 AMM 路由，作为安全缓冲。订单簿执行有时可能会产生尘埃金额——极小的剩余量，小到无法进一步处理。如果没有 AMM 兜底，这些尘埃金额要么需要退还给您（需要您再次兑换），要么被销毁。通过将少量资金路由至 AMM，可确保所有资金得到充分利用，因为 AMM 始终提供持续的流动性。
+