[DOCS] Freshen up README/INSTALL
[DOCS] Freshen up README/INSTALL

This fixes ROOT-10964 .

Co-authored-by: Axel Naumann <cb9efc8f9015dd95c88a8e735ee07ab4f1027cd2@cern.ch>
olifre/root,karies/root,karies/root,root-mirror/root,karies/root,root-mirror/root,root-mirror/root,karies/root,olifre/root,karies/root,root-mirror/root,olifre/root,root-mirror/root,karies/root,karies/root,olifre/root,root-mirror/root,root-mirror/root,root-mirror/root,olifre/root,olifre/root,olifre/root,karies/root,karies/root,karies/root,root-mirror/root,olifre/root,olifre/root,root-mirror/root,olifre/root,karies/root,olifre/root,root-mirror/root