hdf5_ep

[svn-r6781] Purpose:
Add a little more comments on where to put DLL.

Description:
User can put HDF5DLL in the place where the application can find.
It doesn't have to be at system directory.

Solution:
Add comments to "only suggest the user to use system directory".


Platforms tested:
text file, no need to be tested.

Misc. update: