Reorganize top-level doc files for better doc navigation #10113

Job	Run time
omnibus compilations, trigger	1s
omnibus compilations, #1	28m 6s
omnibus compilations, #4	25m 22s
omnibus compilations, #2	30m 2s
omnibus compilations, #3	26m 21s
omnibus compilations, #5	25m 57s
omnibus compilations, #6	27m 9s
omnibus compilations, #7	26m 7s
omnibus compilations, #8	26m 31s
omnibus compilations, #9	26m 39s
omnibus compilations, #11	26m 10s
omnibus compilations, #10	26m 36s
omnibus compilations, #12	24m 19s
omnibus compilations, result	1s
	5h 19m 21s

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