bpo-24318: Rewrite the README PGO section. (GH-6863)


* bpo-24318: Rewrite the README PGO section.

Merged from a phone on an airplane. :)
(cherry picked from commit 93f9a8a5afb58b1d2e4f27bb46d3d4e0fa8c08f0)

Co-authored-by: Gregory P. Smith <greg@krypto.org>
1 file changed