Fix and improve README

[rafamizes]

Turn it more "elegant" by:

• [x] writing a better descripion of the package's purposes
• [x] placing the project logo as the top element
• [x] Initializing the Getting Started section
• [x] EO Principles badge
• [x] Rultor badge
• [x] pub badge
• [x] license badge
• [x] lint badge
• [x] PDD badge
• [x] CI status badge
• [x] codecov badge
• [x] Hits-of-Code badge

[rafamizes]

[0pdd]

@rafamizes the puzzle #8 is still not solved.