update index.md files

[spapastamkou]

This issue concerns the following files:
/pages/index.md
/pages/index.fr.md
/pages/index.de.md

What needs to be done:

• The text in the yaml field: sentences must be updated in all three languages to reflect the identity of Ranke.2 in a few words. Corresponds to the texts that are displayed on the left of the homepage banner.
• I note copyediting problems in current FR texts in first, third and fourth sentences
• The content of the banner exists only in the EN page; the FR and DE pages display "bonjour!"
• The content of the banner needs to be updated anyway in EN to reflect what Ranke.2 is in a a concise and simple way. Currently it reads as follows: "Ranke.2 is a teaching platform for lecturers and students of History to teach how to apply source criticism to digitised and digital born historical sources."
• The text inside the caption of the yaml field: videos needs to be translated in the FR and DE files.
• The links inside the caption of the yaml field: videos are not clickable once displayed in html. - see with @danieleguido / @frederic-reis

[spapastamkou]

J'ai relevé tous les textes à modifier puis traduire dans un document et mettrai à jour ce ticket une fois qu'ils seront prêts.