Update test/README.md

Author: lukewagner

test/README.md

@@ -9,9 +9,9 @@ are enabled by default, they must be explicitly enabled as shown below.)
 
 A single `.wast` test can be run with full backtrace on trap via:
 ```
-WASMTIME_BACKTRACE_DETAILS=1 wasmtime wast -W component-model-async=y -W component-model-async-builtins=y -W component-model-threading=y -W component-model-async-stackful=y the-test.wast
+WASMTIME_BACKTRACE_DETAILS=1 wasmtime wast -W component-model-async=y -W component-model-async-builtins=y -W component-model-threading=y -W component-model-async-stackful=y -W exceptions=y the-test.wast
 ```
 All the tests can be run from this directory via:
 ```
-find . -name "*.wast" | xargs wasmtime wast -W component-model-async=y -W component-model-async-builtins=y -W component-model-threading=y -W component-model-async-stackful=y
+find . -name "*.wast" | xargs wasmtime wast -W component-model-async=y -W component-model-async-builtins=y -W component-model-threading=y -W component-model-async-stackful=y -W exceptions=y
 ```