outdated statements in README intro

[bhaible]

Hi,

The "Intro" section of README.md contains a couple of incorrect statements:

• "unlike the GNU implementation, it can even expand input strings containing so-called sysdep strings into a constant translation table."
  GNU gettext does so too, since version 0.22 (June 2023).

• "in the GNU implementation those are created at runtime"
  Half correct. When processing a .mo file created by msgfmt versions older than 0.22, the sysdep strings are transformed at run time (see intl/loadmsgcat.c).

• "which requires mapping the entire .mo file into read/write memory locations"
  Not true. In the GNU implementation, the .mo file is mmap'ed with PROT_READ (see intl/loadmsgcat.c). Only the hash table (an array of uint32_t numbers) is copied into writable memory locations and augmented with values depending on sysdep strings (see variable inmem_hash_tab in intl/loadmsgcat.c).

Could you please correct the README.md? Thanks.

[rofl0r]

please provide a PR with the desired wording.