Update of the description of the domain-index conversion arrays

The current version of the manual for NEMO 5.0 presents outdated, 1-dimensional local-to-global and global-to-local domain-index conversion arrays, both in Figure 9.6 and in the last paragraph of Section 9.3: the corresponding arrays of NEMO 5.0 are 2-dimensional as they combine conversion variants for various halo widths of the target domain.