Windows phpBin issue for PHP

[dmolsen]

On Windows the PHP version of PL needs to know the path to PHP to start processes like reload behind the scenes. That's done via phpBin config option that isn't included by default. Add docs to explain this issue.

[bradfrost]

Adding @EvanLovely to this. It's a bit to unpack, but it sounds like there's a flag that needs to be included in the docs.