Use PkgConfig as a fallback for finding `NetCDF`

[kieranricardo]

Hi there,

I had some trouble installing ParallelIO on the HPC system I'm on, and I was able fix it by replacing

ParallelIO/CMakeLists.txt

Line 259 in 157e559

find_package (NetCDF REQUIRED COMPONENTS C Fortran)

with

  find_package (NetCDF COMPONENTS C Fortran)
  if (NOT NetCDF_Fortran_FOUND)
    include(FindPkgConfig)
    pkg_check_modules(NetCDF_Fortran REQUIRED IMPORTED_TARGET "netcdf-fortran")
  endif()

It's a non breaking change that'll make ParallelIO more portable so I thought I'd see if there'd be interest in adding this in.

[jedwards4b]

Sure, A PR would be welcome.