[ex-coupling-ff-pm] fix typo

exercises/exercise-coupling-ff-pm/README.md

@@ -340,18 +340,24 @@ bool isOnWall(const GlobalPosition& globalPos) const
 
 In addition, especially for the zero-equation models, any element in the free-flow domain interacts with the walls,
 e.g. this defines the wall distance which is needed to calculate the eddy viscosity.
-To get all these interactions, you have to call `stokesProblem->updateStaticWallProperties()`
+To get all these interactions, you have to call  
+ ```cpp
+ stokesProblem->updateStaticWallProperties()
+ ```
 in `ex_turbulence_coupling_ff-pm.cc`.
 However, there is also a solution-dependent component of these interactions, e.g. for a correct
 damping of the eddy viscosity toward the wall, the velocity gradient at the wall and inside the
 cells is needed.
-These dynamic interactions are to be updated by calling `stokesProblem->updateDynamicWallProperties(stokesSol)`
+These dynamic interactions are to be updated by calling  
+```cpp 
+stokesProblem->updateDynamicWallProperties(stokesSol)
+```
 in the time loop (after `// update dynamic wall properties`).
 
 Compile and run your new coupled problem and take a look at the results in Paraview.
 In addition to the standard variables and parameters, you can now analyze turbulence model specific quantities
-(e.g. the turbulent viscosity `nu_\textrm{t}` or the turbulent diffusivity `D_\textrm{t}`) for the free flow domain.
-In paraview you may compare the magnitude of `D` and `D_\textrm{t}` to see where the transport is affected by turbulence.
+(e.g. the turbulent viscosity $`\nu_\textrm{t}`$ or the turbulent diffusivity $`D_\textrm{t}`$) for the free flow domain.
+In paraview you may compare the magnitude of $`D`$ and $`D_\textrm{t}`$ to see where the transport is affected by turbulence.
 The result for the turbulent viscosity should look like this:
 
 ![](../extradoc/ex_ff-pm-turb_diffusivity.png)