Improve a bit in wording and grammar.

exercises/README.md

 # DuMu<sup>x</sup> course exercises
 
 The DuMu<sup>x</sup> course comprises the following exercises. Each exercise folder contains a detailed description of the tasks
-(best viewed online by following the links) and the header files to work on.
+(best viewed online by following the links) and the source files to work on.
 
 ### [:open_file_folder: Basics](./exercise-basic/README.md)
 
-Based on a scenario, where gas is injected into an aquifer, you will learn how to
+Based on a scenario where gas is injected into an aquifer, you learn how to
 
-* compile and run an executable
-* see the difference of a two phase set-up without component transport compared to a two phase two component set-up
-* set up a new executable
-* set up a non-isothermal test problem based on the isothermal test problem
-* set boundary conditions
+* compile and run an executable,
+* see the difference of an immiscible two-phase model compared to a two-phase two-component model,
+* set up a new executable,
+* set up a non-isothermal test problem based on the isothermal test problem,
+* set boundary conditions.
 
 ### [:open_file_folder: Main file](./exercise-mainfile/README.md)
 
 In this exercise, you learn how to
 
-* find your way in the main file
-* solve a stationary, linear system
-* solve an instationary, linear system
-* solve an instationary, nonlinear system
-* apply analytic differentiation
+* find your way in the main file,
+* solve a stationary, linear system,
+* solve an instationary, linear system,
+* solve an instationary, nonlinear system,
+* apply analytic differentiation.
 
 ### [:open_file_folder: Runtime parameters](./exercise-runtimeparams/README.md)
 
 This exercise covers the following topics: You learn how to
 
-* use different input files with one executable
-* set variables to collect runtime parameters
-* use and change default values for runtime parameters
+* use different input files with one executable,
+* set variables to collect runtime parameters,
+* use and change default values for runtime parameters.
 
 ### [:open_file_folder: Grids](./exercise-grids/README.md)
 
 This exercise guides you through the following tasks:
 
-* apply a global grid refinement
-* change the grid type
-* apply grid zoning and grading
-* read in structured and unstructured grids from external files
+* Apply a global grid refinement,
+* change the grid type,
+* apply grid zoning and grading,
+* read in structured and unstructured grids from external files.
 
 ### [:open_file_folder: Properties](./exercise-properties/README.md)
 
-In this exercise, you learn how to adjust the properties in order to use a customized local residual
+In this exercise, you learn how to adjust the properties in order to use a customized local residual.
 
 ### [:open_file_folder: Fluid systems](./exercise-fluidsystem/README.md)
 
 This exercise covers the handling of phases and components in DuMu<sup>x</sup>. You learn
 
-* how to implement and use a new, customized component
-* how to implement a new fluidsystem
-* change the wettability of the porous medium
+* how to implement and use a new, customized component,
+* how to implement a new fluidsystem,
+* and how to change the wettability of the porous medium.
 
 ### [:open_file_folder: Dune module](./exercise-dunemodule/README.md)
 
 You learn how to
 
-* create a new dune module linked to the dumux module
-* create a new GitLab project
+* create a new dune module which depends on the dumux module,
+* create a new GitLab project.
 
 ### [:open_file_folder: Coupling free and porous medium flow](./exercise-coupling-ff-pm/README.md)
 
@@ -65,11 +65,11 @@ This exercise is related to the [SFB1313 Project Area A](https://www.sfb1313.uni
 
 You learn how to
 
-* use a coupled problem set-up
-* change coupling conditions between the two domains, porous medium flow and free flow
-* change the shape of the interface between the two domains
-* change the model in the porous medium domain
-* change the model in the free flow domain
+* use a coupled problem set-up,
+* change coupling conditions between the two domains, porous-medium flow and free flow,
+* change the shape of the interface between the two domains,
+* change the model in the porous-medium domain,
+* change the model in the free-flow domain.
 
 ### [:open_file_folder: Discrete fracture modeling](./exercise-fractures/README.md)
 
@@ -77,9 +77,9 @@ This exercise is related to the [SFB1313 Project Area B](https://www.sfb1313.uni
 
 You learn how to
 
-* use a problem containing embedded, discrete fractures
-* change the properties of the fractures
-* use domain markers to set internal boundary conditions
+* use a problem containing embedded, discrete fractures,
+* change the properties of the fractures,
+* use domain markers to set internal boundary conditions.
 
 ### [:open_file_folder: Biomineralization](./exercise-biomineralization/README.md)
 
@@ -87,7 +87,7 @@ This exercise is related to the [SFB1313 Project Area C](https://www.sfb1313.uni
 
 You learn how to
 
-* include a chemical reaction in the problem set-up
-* apply the mineralization model, i.e. apply balance equations to possibly changing solid phases
+* include a chemical reaction in the problem setup,
+* apply the mineralization model, i.e. add balance equations to describe dynamic solid phases.
 * compare different simulation results using a programmable filter in Paraview