README.md: Improve text in the "New YaST Module Structure" section
README.md: Improve formatting in the "New YaST Module Structure" section

Make the scheme consistent formatting-wise with a directory tree in the
"Overview" section + add some whitespace.
Merge pull request #397 from yast/readme-improve-new-yast-module-structure

[Review] Request from '' @ 'yast/ycp-killer/readme-improve-new-yast-module-structure'