lib, doc: rename readme.md to README.md

PR-URL: #52471
Reviewed-By: Antoine du Hamel <[email protected]>
Reviewed-By: Deokjin Kim <[email protected]>
Reviewed-By: Luigi Pinca <[email protected]>
Reviewed-By: Ulises Gascón <[email protected]>
Reviewed-By: Marco Ippolito <[email protected]>

Author: avivkeller