[Roadmap] Improve Basics section

[matks]

• [x] Introduction ✅
• [x] Installation ✅
• [ ] Understanding PrestaShop 🔴
• [x] Staying up-to-date ✅

We should add a "Understanding PrestaShop" page/section following example of Drupal (see https://www.drupal.org/docs/understanding-drupal)

Other pages/sections seem quite complete for now.

[MeKeyCool]

.