[benchmark#doc] Added a description about the benchmark for the permeability model for EDZ

web/content/docs/benchmarks/hydro-mechanics/PermeabilityMohrCoulombFailureIndexModel.pandoc

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+date = "2020-06-11"
+title = "Permeability in EDZ"
+weight = 151
+project = "HydroMechanics/FailureIndexDependentPermeability/quad_with_half_hole.prj"
+author = "Wenqing Wang"
+
+[menu]
+  [menu.benchmarks]
+    parent = "hydro-mechanics"
+
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+
+{{< data-link >}}
+
+For the description of the benchmark and its related permeability model,
+  please read [the PDF](../PermeabilityMohrCoulombFailureIndexModel.pdf).
+
+For a full document of the failure index dependent
+ permeability model, benchmark and its the implementation in ogs6, etc.,
+  please visit the Overleaf site:
+ <https://www.overleaf.com/read/qjfmysnsvqwb>
+which contains LeTeX source of the documentation as well.
+ If you want to edit the document on Overleaf site, please contact us.