experiments/run.py: support out-of-tree runs with default params

Currently --repo, which is used to find simulators etc., defaults to '..',
which only works when executing in the 'experiments' directory in the simbricks
repo. Instead we make this relative to the run.py-file's path.

experiments/run.py

@@ -109,7 +109,7 @@ def parse_args() -> argparse.Namespace:
         '--repo',
         metavar='DIR',
         type=str,
-        default='..',
+        default=os.path.dirname(__file__) + '/..',
         help='SimBricks repository directory'
     )
     g_env.add_argument(