Rewrite All_About_Descriptions_Graphics_and_Screenshots.md

Previously, this page was confusing, lacking information and disorganized. So I rewrote it by combining the following sources:

• https://gitlab.com/snippets/1895688 and https://gitlab.com/snippets/1901490
• fdroidserver/fdroidserver/update.py
• https://f-droid.org/en/2019/03/26/the-latest-tab-now-highlights-good-descriptions.html
• current page

I hope I understood what I read correctly so that there are no mistakes in the rewrite.