updated readme

Author: VibhorCodecianGupta

README.md

@@ -26,6 +26,7 @@ Currently we have following images -
  - [java8](containers/java8)
  - [nodejs6](containers/nodejs6)
  - [nodejs](containers/nodejs8)
+ - [php7](containers/php7)
  - [py2](containers/py2)
  - [py3](containers/py3)
  - [ruby](containers/ruby)