Add section Contributing. #732

Job	Run time
Julia 1 - windows-latest - x64 - push	12m 41s
Julia 1.10 - ubuntu-latest - x64 - with code coverage	4m 4s
Julia 1 - ubuntu-latest - x64 - push	8m 48s
Julia 1.10 - ubuntu-latest - x64 - push	9m 9s
Documentation	6m 18s
Julia pre - ubuntu-latest - x64 - with code coverage	4m 7s
Julia 1.11 - ubuntu-latest - x64 - with code coverage	4m 6s
Julia pre - ubuntu-latest - x64 - push	8m 59s
Julia 1 - macOS-latest - aarch64 - push	6m 29s
	1h 4m 41s

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