Add documentation node for PHP error_reporting level.

When PHP's error_reporting level includes the E_STRICT level (2048) Ushahidi breaks and reports "Strict Mode Error" warnings and is unable to load any pages.

This PR only documents this issue.  The ideal solution would be to adhere to strict mode limitations, and as a second choice it would be to detect the E_STRICT error_reporting level and warn about this before displaying "Strict Mode Error".

Tested on Debian Wheezy with a custom built PHP-5.4.25 using PHP-FPM + Nginx.