Update results script with current expected binary paths

Also update README.md to reflect the current reality of building the
runner.

README.md

@@ -18,23 +18,19 @@ Dependencies are:
 
 ## Usage
 
-To clone test262, clone SerenityOS, build Lagom, and build `libjs-test262-runner`, run:
+To clone test262, clone serenity and build Lagom run:
 
 ```console
 ./setup.sh
 ```
 
-The repositories will only be cloned if they don't exist yet locally, so you
-can use this script for development of the test runner as well.
-
-If `SERENITY_SOURCE_DIR` is set, it will be used instead. However, if the Lagom
-build directory already exists, the script will not touch your build in that
-case, so you'll need to build `libLagom.a` yourself.
+The repositories will only be cloned if they don't exist yet locally.
+If `SERENITY_SOURCE_DIR` is set, it will be used to compile the runner instead of cloning serenity.
 
 Once that's done, run:
 
 ```console
-python3 main.py --libjs-test262-runner ./Build/_deps/lagom-build/bin/test262-runner --test262-root ./test262/
+python3 main.py --libjs-test262-runner ./Build/bin/test262-runner --test262-root ./test262/
 ```
 
 ## Options

run_all_and_update_results.py

@@ -30,13 +30,21 @@ def get_git_commit_timestamp(path: Path) -> int:
 
 
 def find_lagom_executable(test262_path: Path, serenity_path: Path, name: str):
-    executable_path = test262_path / f"Build/_deps/lagom-build/bin/{name}"
-    if not executable_path.exists():
-        executable_path = serenity_path / f"Build/lagom/bin/{name}"
-        if not executable_path.exists():
-            executable_path = serenity_path / f"Build/lagom/Meta/Lagom/bin/{name}"
+    # Build/bin: Local build
+    # serenity_path / Build/lagom/bin: Meta/Lagom source dir
+    # _deps: Local build before 2023-08-13
 
-    return executable_path
+    paths = [
+        test262_path / f"Build/bin/{name}",
+        serenity_path / f"Build/lagom/bin/{name}",
+        test262_path / f"Build/_deps/lagom-build/bin/{name}",
+    ]
+
+    for path in paths:
+        if path.exists():
+            return path
+
+    raise RuntimeError(f"Unable to find {name}")
 
 
 def main() -> None: