Document php vulnerabilities

Security: CVE-2015-8879
Security: CVE-2016-5385
Security: CVE-2016-5399
Security: CVE-2016-6288
Security: CVE-2016-6289
Security: CVE-2016-6290
Security: CVE-2016-6291
Security: CVE-2016-6292
Security: CVE-2016-6294
Security: CVE-2016-6295
Security: CVE-2016-6296
Security: CVE-2016-6297