GEOS php bindings install instructions changed

As of geos 3.6.0, the PHP binding has its own repository.

This changes the installation instructions and it would help if this module could update to the newer instructions. You now install libgeos and the PHP bindings separately.

Many distros will have a package for libgeos. On Ubuntu 16.04 it is libgeos-c1v5 and you also need libgeos-dev temporarily whilst building the PHP extension.

The instructions in the PHP binding repository are clear as far as they go, but they don't cover loading the module. The instructions for that are the same as they were, for example see http://www.saintsjd.com/2014/06/05/howto-intsall-libgeos-with-php5-bindi..., starting with "cat > /etc/php5/mods-available/geos.ini"