[RM/Test] Added a short description about the Liakopoulos benchmark

web/content/docs/benchmarks/richards-mechanics/liakopoulos.md

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+project = "RichardsMechanics/LiakopoulosHM/liakopoulos.prj"
+author = "Wenqing Wang"
+title = "A test based on the Liakopoulos experiment"
+date = 2020-10-21T15:07:13+02:00
+weight = 153
+
+[menu]
+  [menu.benchmarks]
+    parent = "richards-mechanics"
+
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+This benchmark simulates the Liakopoulos experiment
+  [[1]](#1)
+ with an assumption of  the Richards' flow  coupled with deformation.
+
+{{< data-link >}}
+
+* Saturation profile:
+{{< img src="../liak_S.png" >}}
+* Vertical displacement profile:
+{{< img src="../liak_uy.png" >}}
+
+
+## References
+<a id="1">[1]</a>
+Liakopoulos, Aristides C (1965).
+Variation of the permeability tensor ellipsoid in homogeneous anisotropic soils.
+Water Resources Research, 1(1), 135--141.