update contributing guide for pipeline skips

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4 jobs for add-pipeline-skips in 7 minutes (queued for 17 minutes and 31 seconds)
Status Job ID Name Coverage
  .Pre
passed #1185900
make-dist

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passed #1185901
make-dist:lal

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  Lint
passed #1185903
lint:coala

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passed #1185902
lint:python

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