Bump version of cldr to 45 in README.md

[WurmPeter]

Just a small correction: The introduction paragraph still said "As of April 28th 2023 and ex_cldr Version 2.37.0, ex_cldr is based upon [CLDR version 43.0]http://cldr.unicode.org/index/downloads/cldr-43)."

Changed to "As of August 16th 2024 and ex_cldr Version 2.40.1, ex_cldr is based upon CLDR version 45.0."