update readme

README.md

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 **Invert4geom** is a Python library for performing 3D geometric gravity inversions, where the aim is to recover the geometry of a density contrast.
 
-Typically use cases include modeling the Moho, the sediment-basement contact, or bathymetry. These density contrasts are represented by a layer of vertical right-rectangular prisms. 
+Typical use cases include modeling the topography of the Moho, the sediment-basement contact, or bathymetry. These density contrasts are represented by a layer of vertical right-rectangular prisms. Since we use vertical prisms, they don't take the curvature of the Earth into account. For large-scale applications, such as continental studies, it would be better to use tesseroids instead of prisms.
+
+See the [overview](overview.md) for further description of this package and what it can be used for.
+
+The tutorials
 
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