Merge branch 'fix/ex-readme' into 'master'

[ex][model] update description in readme

See merge request !180

exercises/README.md

@@ -47,10 +47,10 @@ In this exercise, you learn how to adjust the properties in order to use a custo
 
 ### [:open_file_folder: Model](./exercise-model/README.md)
 
-This exercise covers the implementation of new models DuMu<sup>x</sup>. You learn
+This exercise covers the implementation of new models in DuMu<sup>x</sup>. You learn
 
 * how to design a nonlinear diffusion equation model from scratch (almost)
-* how to implement a local residual using the a minimal model design
+* how to implement a local residual using a minimal model design
 * use DuMu<sup>x</sup> to denoise an image (!)