adding new item for security section (public-apis#826)

* adding new item for security section

* Update README.md

Author: grepit

README.md

@@ -629,6 +629,7 @@ API | Description | Auth | HTTPS | CORS |
 | [AXFR Database](http://api.axfrcheck.com) | AXFR public database | No | No | Unknown |
 | [FilterLists](https://filterlists.com/api) | Lists of filters for adblockers and firewalls | No | Yes | Unknown |
 | [HaveIBeenPwned](https://haveibeenpwned.com/API/v2) | Passwords which have previously been exposed in data breaches | No | Yes | Unknown |
+| [National Vulnerability Database](https://nvd.nist.gov/vuln/Data-Feeds/JSON-feed-changelog) | U.S. National Vulnerability Database | No | Yes | Unknown |
 | [SecurityTrails](https://securitytrails.com/corp/apidocs) | Domain and IP related information such as current and historical WHOIS and DNS records | `apiKey` | Yes | Unknown |
 | [Shodan](https://developer.shodan.io/) | Search engine for Internet connected devices | `apiKey` | Yes | Unknown |
 | [UK Police](https://data.police.uk/docs/) | UK Police data | No | Yes | Unknown |