Improvement for the available translations listed on each readme

[kmacedovarela]

Changes

Related to #32

• 🧹 List of available translations
• 🧹 Adjustments of the headings structures on the main readme

/kind cleanup

Release Note

- The list of available translations is now cleaner and won't occupy to much space when the list of options grow
- Standardized across all english files
- Instead of using, for instance, `pt-BR`, each link is now written on the referred language `Português (Portuguese)`
- Link to the list of contributors added on every reference of the translation's contributions. 
- The translations section was added to every chapter to facilitate the inclusion of incoming new languages added by contributors.