Refined CODE_OF_CONDUCT.md and CONTRIBUTING.md

[XuehaoSun]

Type of Change

docs refine

• CODE_OF_CONDUCT.md
• CONTRIBUTING.md

Description

• Rename contributions.md --> CONTRIBUTING.md, follow the github docs contribution guidelines
• Add content list
• Update email address
• Remove duplicate content
• Format files
• others: add aia to the spell-check dict

Expected Behavior & Potential Risk

the expected behavior that triggered by this PR

How has this PR been tested?

how to reproduce the test (including hardware information)

Dependency Change?

any library dependency introduced or removed