Add geometry image

Closes #21

fsi-workflow/00_geometry/tasks.md

@@ -21,6 +21,8 @@ We will use the following software:
 
 ## Task 0: Prepare the geometry
 
+![Cross-section of the geometry](images/wing_sect.png){#fig:t0-geometry width=7cm}
+
 We will simulate fluid-structure interaction of a very simple airfoil, in 3D. [NACA airfoils](https://en.wikipedia.org/wiki/NACA_airfoil) are standardized designs that are popular in designing aircraft wings.
 Our case is slightly derived from the following paper:
 
@@ -39,8 +41,6 @@ You'll notice that two different file formats are provided: a `.stl` file and a
 
 When meshing a flow domain, we need to consider whether we are simulating external or internal flow. In this case, we are considering an external flow: we will use the solid geometry to generate the **solid mesh**, and we will subtract it from a sufficiently large box to generate the **fluid mesh**.
 
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 ### Notes on file formats
 
 You might wonder: "Why two formats?".