Document that HDF5 >1.10 is required for reading SWMR file

Created by: matthew-d-jones

From the HDF5 documentation:

Please note that HDF5 files created with SWMR access cannot not be read by the tools based on the HDF5 1.8 libraries due to the file format changes in the HDF5 1.10 versio n of the library.

This should be mentioned in the README as tools such as HDFView can fail to open files and give no error message in the case that SWMR was used. h5py installed via pip, and Mantid will also fail to open files written with SWMR.