Grammar: add the word "of" in functors tutorial

Author: neuroevolutus

data/tutorials/language/1ms_01_functors.md

@@ -63,7 +63,7 @@ Here is how this reads (starting from the bottom, then going up):
 
 **Note**: Most set operations need to compare elements to check if they are the same. To allow using a user-defined comparison algorithm, the `Set.Make` functor takes a module the specifies both the element type `t` and the `compare` function. Passing the comparison function as a higher-order parameter, as done in `Array.sort`, for example, would add a lot of boilerplate code. Providing set operations as a functor allows specifying the comparison function only once.
 
-Here is an example how to use `Set.Make`:
+Here is an example of how to use `Set.Make`:
 
 **`funkt.ml`**