source of the find petsc module

AMDiS/FindPETSc.cmake

 # - Try to find PETSc
 # Once done this will define
+# source: https://github.com/jedbrown/cmake-modules/blob/master/FindPETSc.cmake
 #
 #  PETSC_FOUND        - system has PETSc
 #  PETSC_INCLUDES     - the PETSc include directories