README - update with Haskell Platform installation instructions

Signed-off-by: Pang Yan Han <pangyanhan@gmail.com>
Update cabal version to 1.18.0.5

Signed-off-by: Pang Yan Han <pangyanhan@gmail.com>
Use Hakyll 4.6.2.0

Signed-off-by: Pang Yan Han <pangyanhan@gmail.com>
setup_haskell_sandboxes - only setup hakyll

Signed-off-by: Pang Yan Han <pangyanhan@gmail.com>