[exercise-coupling-ff-pm] Improve description

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

@@ -12,7 +12,7 @@ Free flow is modeled in the upper subdomain, while the lower subdomain models a
 
 * Navigate to the directory `exercises/exercise-coupling-ff-pm`
 
-There are three sub folders: `interface`, `models` and `turbulence`.
+There are three sub folders: `interface` (Exercise 1), `models` (Exercise 2) and `turbulence` (Exercise 3).
 
 The problem-related files for this exercise are:
 * Three __main files__ for the three sub-tasks :`ex_interface_coupling_ff-pm.cc`, `ex_models_coupling_ff-pm.cc`, `ex_turbulence_coupling_ff-pm.cc`,
@@ -166,7 +166,7 @@ Make sure, that you have uncommented the lines including the gridcreators in bot
 
 and do the changes in the respective lines for the `Grid` property.
 
-The problem should now compile and run. However, an error occurs due to the coupling conditions.
+The problem should now compile. However, an error occurs due to the coupling conditions.
 So far, we assumed a flat interface, therefore the normal momentum coupling condition
 
  $`[\sigma \cdot \mathbf{n}]^{FF} = p^{PM}`$