GitHub: Update Readme for consistency

[0x5bfa]

Description

As the title.

Preview: https://github.com/0x5bfa/WinUI-Gallery/blob/5bfa/GitHub-ConsistentReadmeHeader/README.md

Motivation and Context

How Has This Been Tested?

Screenshots (if appropriate):

Types of changes

• [ ] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)

[0x5bfa]

@niels9001 Hi! Is there a plan to update Dev Home repo README to have this hero? It looks great!