Clarify boundary conditions in README.md

Updated the description of the surrogate boundary conditions and clarified the assignment of the volumetric term.

Author: NickNick9

iga/use_cases/laplacian_sbm_3d_bunny/README.md

@@ -1,14 +1,14 @@
 # Use Case IGA - 3D Laplacian on the Stanford Bunny with SBM
 
-Short description
-
 This example solves a stationary 3D Laplacian problem with the Surrogate Boundary Method (SBM) in the IGA Application. The embedded boundary is the Stanford bunny imported from `bunny.mdpa`, while the analysis is carried out on a structured background NURBS volume.
 
+<img width="1100" height="900" alt="bunny" src="https://github.com/user-attachments/assets/b5a70769-796b-4035-a307-05bc327a075b" />
+
 The manufactured solution used for validation is:
 
 `T(x, y, z) = sin(x) * sinh(y) * cos(z)`
 
-The same field is prescribed on the surrogate boundary, and the corresponding volumetric term is assigned through `HEAT_FLUX`.
+The same field is prescribed on the true boundary, and the corresponding volumetric term is assigned.
 
 Files
 - `ProjectParameters.json`
@@ -40,6 +40,7 @@ python3 plot_conditions.py
 ```
 
 `run_and_post.py` runs the analysis, prints the absolute and normalized L2 errors, and plots the error distribution at the element integration points.
+<img width="969" height="748" alt="bunny_error" src="https://github.com/user-attachments/assets/a6070ca2-7231-424a-b265-d90b74f3b4f5" />
 
 `convergence.py` performs a mesh-refinement study by changing the number of knot spans of the background NURBS volume.