Add capsule as an example of a simple geometry (#313)

examples/capsule.py

@@ -0,0 +1,31 @@
+r"""
+Capsule geometry example
+-------------------------
+
+Capsule geometry example.
+
+"""
+
+# sphinx_gallery_thumbnail_number = 3 # noqa:ERA001
+
+from __future__ import annotations
+
+import pyvista as pv
+
+import skgmsh as sg
+
+edge_source = pv.Capsule(resolution=10)
+edge_source.merge(pv.PolyData(edge_source.points), merge_points=True, inplace=True)
+edge_source.plot(show_edges=True, color="white")
+
+# %%
+# Create a 3D mesh from the edge source.
+
+alg = sg.Delaunay3D(edge_source)
+alg.mesh.shrink(0.9).plot(show_edges=True, color="white")
+
+# %%
+# Change the cell size of the mesh.
+
+alg.cell_size = 0.25
+alg.mesh.plot(show_edges=True, color="white")