Natha's Numenera French Sheet v2.01

- Slight change to the sheet : more detailed "Advancements" section, with fields to keep track of the 24 possible advancements
- New readme.md :
  - translated to french 
  - link to the english version
  - cleaner layout
  - more detailed help/setting guide
- New help screenshot
- New preview image (thus, updated sheet.json)