Update Exercise 1 (typo)

ex1/README.md

@@ -38,7 +38,7 @@ Start with a simple elevation filter ([`vtkElevationFilter`](https://vtk.org/doc
 
 Note however, that the elevation only depends on a direction. Still, please use sensible values (e.g. corresponding to the height of the cylinder). 
 
-Generally, to connect to filters, you need to use a construction of the form
+Generally, to connect two filters, you need to use a construction of the form
 ```
 filter2->SetInputConnection( filter1->GetOutputPort() )
 ```