HDF page: add information about HDF4 and HDF5 libraries

[GreatEmerald]

During the project week, I ran into a problem that MODIS data is in the HDF4 format, however, it couldn't be read by GDAL, as it assumed it was in the NetCDF format instead. Turns out that GDAL can be compiled either with HDF4 support, or with HDF5 + NetCDF support (see https://trac.osgeo.org/gdal/wiki/HDF#IncompatibilitywithNetCDFLibraries). The former was default before the HDF5 format was popular, and the latter is the default nowadays, with HDF4 not built by default any more (http://r-sig-geo.2731867.n2.nabble.com/OSX-rgdal-GDAL-drivers-and-HDF4-td7588400.html). Older OSs like OSGeo Live thus could read HDF4 images, whereas newer OSs like openSUSE Leap cannot (without having to recompile GDAL from source, or, like I ended up doing, creating a forked package like this). So adding some information to that end to the HDF page is probably a good idea.

[janverbesselt]

good idea, and ok for me to add more information about that.