update README.md.

Signed-off-by: 葛峻恺 <202115006@mail.sdu.edu.cn>

README.md

@@ -17,7 +17,9 @@ A PyTorch-based implementation of a source-independent full waveform inversion (
 GPR-SIDL-inv/
 │
 ├── dataset/                   # Training/testing data and synthetic datasets
+
 ├── field_data/                 # Network architectures
+
 ├── gprMax/                  # Data processing, waveform simulation, etc.
 ├── IMG/                # Training script
 ├── impulse/                 # Inversion / prediction script