Docs: Add warnings about contract checks in execution/refunds flows

[mmv08]

From the audit report

[coveralls]

Pull Request Test Coverage Report for Build 4488298056

• 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 98.536%

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Totals
Change from base Build 4479857320:	0.0%
Covered Lines:	315
Relevant Lines:	316

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💛 - Coveralls