docs: design philosophy

[fmunteanu]

Objective

Minor improvements to Design Philosophy page, added Behavioral Science section.

Scope

• Bug (resolves an issue)
• Enhancement (improves existing functionality)
• Feature (adds new functionality)
• Documentation (adds or improves documentation)

Impact

• Non-breaking (backwards compatible)
• Breaking (backwards incompatible, impacts end-user)

Checklist

• My code follows the contributing guidelines of this project
• I have performed a self-review of my code
• I have made corresponding changes to the documentation
• My changes generate no new issues or warnings