ICU-22404 Improve documentation of segmentation rules #391

Job	Run time
clang-valgrind-test	16m 6s
clang-valgrind-intltest (utility)	9m 16s
clang-valgrind-intltest (normalize)	9m 24s
clang-valgrind-intltest (collator)	8m 28s
clang-valgrind-intltest (regex)	6m 28s
clang-valgrind-intltest (format)	31m 38s
clang-valgrind-intltest (translit)	7m 25s
clang-valgrind-intltest (rbbi)	13m 39s
clang-valgrind-intltest (rbnf)	9m 50s
clang-valgrind-intltest (rbnfrt)	9m 16s
clang-valgrind-intltest (icuserv)	6m 9s
clang-valgrind-intltest (idna)	6m 23s
clang-valgrind-intltest (convert)	10m 11s
clang-valgrind-intltest (rbnfp)	7m 2s
clang-valgrind-intltest (csdet)	7m 51s
clang-valgrind-intltest (spoof)	6m 42s
clang-valgrind-intltest (bidi)	6m 25s
	2h 52m 13s

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