Update index.md

[kyrillospan]

This pull request updates the introductory section of the docs/en/index.md file to improve clarity and foster a more welcoming and collaborative tone. The changes focus on refining the language and messaging to better communicate the community's mission and encourage contributions.

Content and messaging improvements:

• Reworded the background section to clearly state the purpose of the PyGreece Community Knowledge Base and emphasize openness and collaboration.
• Updated the sharing knowledge section to clarify the goal of openly sharing resources and to encourage contributions, with a promise of forthcoming instructions for new contributors.Fix typos and improve intro text

[thepetk]

lgtm