Add README about fuzz testing

Author: kateinoigakukun

FuzzTesting/.gitignore

@@ -0,0 +1,38 @@
+# Fuzz Testing
+
+This subdirectory contains some [libFuzzer](https://www.llvm.org/docs/LibFuzzer.html) fuzzing targets for WasmKit.
+
+> [!WARNING]
+> libFuzzer does not work with the latest Swift runtime library on macOS for some reason. Run the fuzzing targets on Linux for now.
+
+## Requirements
+
+- [Open Source Swift Toolchain](https://swift.org/install) - Xcode toolchain does not contain fuzzing supoort, so you need to install the open source toolchain.
+- [wasm-tools](https://github.com/bytecodealliance/wasm-tools) - Required to generate random seed corpora
+
+
+## Running the Fuzzing Targets
+
+1. Generate seed corpora for the fuzzing targets:
+    ```sh
+    ./fuzz.py seed
+    ```
+2. Run the fuzzing targets, where `<target>` is one of the fuzzing targets available in `./Sources` directory:
+    ```sh
+    ./fuzz.py run <target>
+    ```
+3. Once the fuzzer finds a crash, it will generate a test case in the `FailCases/<target>` directory.
+
+
+## Reproducing Crashes
+
+To reproduce a crash found by the fuzzer
+
+1. Build the fuzzer executable:
+    ```sh
+    ./fuzz.py build <target>
+    ```
+2. Run the fuzzer executable with the test case:
+    ```sh
+    ./.build/debug/<target> <testcase>
+    ```

FuzzTesting/README.md

@@ -29,14 +29,16 @@ def main():
     # Subcommands
     subparsers = parser.add_subparsers(required=True)
 
+    available_targets = list(os.listdir('Sources'))
+
     build_parser = subparsers.add_parser('build', help='Build the fuzzer')
     build_parser.add_argument(
-        'target_name', type=str, help='Name of the target')
+        'target_name', type=str, help='Name of the target', choices=available_targets)
     build_parser.set_defaults(func=build)
 
     run_parser = subparsers.add_parser('run', help='Run the fuzzer')
     run_parser.add_argument(
-        'target_name', type=str, help='Name of the target')
+        'target_name', type=str, help='Name of the target', choices=available_targets)
     run_parser.add_argument(
         '--skip-build', action='store_true',
         help='Skip building the fuzzer')