[SECURITY] Add more guidelines for security disclosures

[fxamacker]

Updates onflow/flow-go#8042

Added more guidelines:

Before submitting a security report, please review your source code included in the report. For example, please check if function calls return any errors and avoid calling functions on a nil object.

Even if the bug report relied on an obvious mistake made by the team submitting the report, it still takes time to review the other content, just in case it includes a real bug.

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• Targeted PR against main branch
• Linked to Github issue with discussion and accepted design OR link to spec that describes this work
• Code follows the standards mentioned here
• Updated relevant documentation
• Re-reviewed Files changed in the Github PR explorer
• Added appropriate labels

[fxamacker]

@turbolent PTAL 🙏

If security reports contain obvious bugs that can be spotted at a quick glance, then I think there is a chance that some reviewer in the future might not examine the report's other content as thoroughly as they should.