update README.md.

Signed-off-by: 刘明宏 <liuminghong@mail.sdu.edu.cn>

README.md

@@ -7,15 +7,18 @@ To address the high computational cost of 3D modeling, em3d-MT integrates a dire
 
 #### software framework
 
-This section provides detailed instructions for installing and configuring the em3d-MT package. The software is developed in MATLAB and requires proper setup of external solvers for efficient computation.
+# This section provides detailed instructions for installing and configuring the em3d-MT package. The software is developed in MATLAB and requires proper setup of external solvers for efficient computation.
 #### 2.1 System Requirements
 Operating System: Windows or Linux
 MATLAB Version: R2023a (or later)
 Memory: The actual memory usage depends on model size and number of frequencies. 
 #### 2.2 Required Software
+
 MATLAB (R2023a or later): The core environment in which em3d-MT operates.
+
 em3d-MT relies on several external tools and libraries to facilitate 3D geological modeling and mesh generation. The following software is required for proper functionality:
 GeoMesh
+
 For 3D geological modeling and mesh generation, GeoMesh is used. This is an open-source tool specifically designed for electromagnetic (EM) modeling, based on the COMSOL Multiphysics and MATLAB interface (Liu et al., 2024). GeoMesh generates unstructured tetrahedral meshes, which are ideal for representing complex subsurface structures in the forward modeling process. You can find the tool at https://gitee.com/sduem/geomesh
 Additionally, em3d-MT supports two types of direct solvers for solving the finite element system:
 Panua-Pardiso: