Update README.md with the link to the HPC repo.

README.md

@@ -76,7 +76,7 @@ In order to use the library, two changes are required:
 
   The cache update frequency is set for both matrix and preconditioner in the petsc/caching subdict.
 
-An example is reported below. Other examples can be found in the tutorial folder.
+An example is reported below. Other examples can be found in the tutorial folder or in the [HPC repo](https://develop.openfoam.com/committees/hpc).
 For more details, the user can read the paper [1].
 
     solvers