improve contributing docs

[n2ygk]

Description of the Change

Improve documentation for contributors and project leads.

Checklist

• PR only contains one change (considered splitting up PR)
• unit-test added
• documentation updated
• CHANGELOG.md updated (only for user relevant changes)
• author name in AUTHORS

[coveralls]

Pull Request Test Coverage Report for Build 1480

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-94.8%) to 0.0%

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Totals
Change from base Build 1478:	-94.8%
Covered Lines:	0
Relevant Lines:	0

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💛 - Coveralls

[coveralls]

Pull Request Test Coverage Report for Build 1480

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 94.806%

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Totals
Change from base Build 1478:	0.0%
Covered Lines:	1296
Relevant Lines:	1367

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💛 - Coveralls