doc: Add installation instructions for building with meson

Author: samay sharma <smilingsamay@gmail.com>
Reviewed-by: Justin Pryzby <pryzby@telsasoft.com>
Reviewed-by: Andres Freund <andres@anarazel.de>
Reviewed-by: Nazir Bilal Yavuz <byavuz81@gmail.com>
Reviewed-by: Peter Eisentraut <peter.eisentraut@enterprisedb.com>
Discussion: https://www.postgresql.org/message-id/flat/CAJxrbywFPcgC4nP_v+HHPhaYSWX2JL8FZXY2aFOZxXxTkTJJPw@mail.gmail.com

Author: petere