docs: update fusionreport score calculation documentation Resolves nf-core#555 #1598

Job	Run time
24.04.2 \| test_stub \| docker	10m 47s
24.04.2 \| test_build \| docker	27m 6s
latest-stable \| test_stub \| docker	10m 18s
latest-stable \| test_build \| docker	31m 9s
	1h 19m 20s

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