Create INSTALL file using Pandoc

Create INSTALL file using Pandoc

Replace using lynx with using pandoc.  Pandoc creates better looking
output and it avoids the delicate locale/encoding issues of lynx because
it always uses UTF-8 for both input and output.

Note: requires Pandoc >=1.13

Discussion: https://www.postgresql.org/message-id/flat/dcfaa74d-8037-bb32-f9e0-3fea7ccf4551@2ndquadrant.com/
Reviewed-by: Mi Tar <mmitar@gmail.com>