[3.10] bpo-45788: Link sys.prefix doc to 'Installation paths' (GH-29606)

... To the Installation paths section of the sysconfig doc.
(cherry picked from commit 4575c01b750cd26377e803247c38d65dad15e26a)

Co-authored-by: Terry Jan Reedy <tjreedy@udel.edu>
3 files changed