pgsql: 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: /messages/by-id/dcfaa74d-8037-bb32-f9e0-3fea7ccf4551@2ndquadrant.com/
Reviewed-by: Mi Tar <mmitar@gmail.com>

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/96b8b8b6f9d8de4af01a77797273ad88c7a8e32e

Modified Files
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doc/src/sgml/Makefile | 14 +++-----------
doc/src/sgml/docguide.sgml | 4 +++-
2 files changed, 6 insertions(+), 12 deletions(-)