Add README.rst to explain project goal

README.rst

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+Motivation
+==========
+
+`PyVista`_ accessors for `Gmsh`_ to generate 3D finite element mesh.
+
+.. _PyVista: https://docs.pyvista.org/version/stable/
+.. _Gmsh: https://gmsh.info/
+
+Usage
+=====
+
+.. code-block:: python
+
+    >>> import pyvista as pv
+    >>> import pvgmsh
+
+We can define the surface using PyVista.
+
+.. code-block:: python
+
+    >>> square = pv.Polygon(n_sides=4, radius=8, fill=False)
+    >>> square = square.rotate_z(45, inplace=False)
+
+We can then generate a 2D mesh.
+
+.. code-block:: python
+
+    >>> tess = pvgmsh.frontal_delaunay_2d(edge_source=square, mesh_size=1.0)
+
+To visualize the model we can use PyVista.
+
+.. code-block:: python
+
+    >>> plotter = pv.Plotter()
+    >>> _ = plotter.add_mesh(tess, show_edges=True)
+    >>> plotter.show(cpos="xy")
+
+.. image:: https://github.com/pyvista/pyvista-gmsh/raw/main/frontal_delaunay_2d_01.png