Elastic Beanstalk supported platforms

[iainelder]

https://docs.aws.amazon.com/elasticbeanstalk/latest/platforms/platforms-supported.html

https://docs.aws.amazon.com/elasticbeanstalk/latest/platforms/platforms-retiring.html

[iainelder]

I'll make a PR for this later.

[globart]

@iainelder reminder

[iainelder]

@globart see #133 . Thanks!