feat: harden trading SDK examples

examples/README.md

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+# sol-trade-sdk Examples
+
+[中文](README_CN.md)
+
+Run commands from the repository root with `cargo run --package <name>`. Read the example's README before running it: many protocol examples contain placeholder keys or addresses and submit real mainnet transactions after configuration.
+
+## Choose an example
+
+| Category | Examples |
+|---|---|
+| Start here | `simple_trading`, `trading_client`, `shared_infrastructure` |
+| Low latency | `pumpswap_trading`; also read `../docs/LOW_LATENCY_BOTS.md` |
+| PumpFun streams | `pumpfun_sniper_trading`, `pumpfun_copy_trading` |
+| Other DEXs | `pumpswap_direct_trading`, `bonk_*`, `raydium_*`, `meteora_*` |
+| Transaction construction | `address_lookup`, `nonce_cache`, `middleware_system`, `seed_trading` |
+| Utilities | `gas_fee_strategy`, `wsol_wrapper`, `cli_trading` |
+
+## Safety boundary
+
+- Files containing `use_your_*` or `your_*_here` are templates. Replace every placeholder before running.
+- `simple_trading` and `gas_fee_strategy` do not submit a swap as shipped. Most other trading examples can.
+- Event-driven templates that create the client or fetch blockhash/state inside the callback demonstrate protocol mapping, not the final low-latency architecture.
+- Never commit private keys. Use environment variables or a secure keystore in real applications.
+- Use `SimpleBuyParams` / `SimpleSellParams` for new integrations unless low-level account flags are specifically required.
+
+Each example directory contains matching English and Chinese documentation.