Updated installation instructions
Updated installation instructions

This documents following final setup:
   - postgis 1.5.3 from ubuntugis-unstable PPA
   - mapnik 2.0.0 with libboost 1.46 from thomasjj PPA

Tested:
   - CLI frontend
   - maposmatic web frontend

Signed-off-by: David Decotigny <ce9ed66d82df7ce028a8623498350e2fb4412132@maposmatic.org>

maposmatic/ocitysmap,dittaeva/ocitysmap,dittaeva/ocitysmap,maposmatic/ocitysmap,maposmatic/ocitysmap