doc: update wasi-threads readme

Author: eloparco

samples/wasi-threads/README.md

@@ -26,6 +26,7 @@ $ ./iwasm wasm-apps/exception_propagation.wasm
 ## Run samples in AOT mode
 ```shell
 $ ../../../wamr-compiler/build/wamrc \
+    --enable-multi-thread \
     -o wasm-apps/no_pthread.aot wasm-apps/no_pthread.wasm
 $ ./iwasm wasm-apps/no_pthread.aot
 ```