chore: simplify report filenames and update readme links. #6

Job	Run time
R-CMD-check (macos-latest, release)	4m 41s
R-CMD-check (ubuntu-latest, release)	13m 30s
R-CMD-check (macos-latest, devel)	4m 6s
R-CMD-check (ubuntu-latest, devel)	15m 2s
	37m 19s

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