Update readme.md on how to setup play 2.4.2

[ronaldwidha]

The readme.md is out of date and causing specifically 2 known issues discussed in the following threads:

• https://github.com/typesafehub/play-plugins/issues/156
• https://github.com/typesafehub/play-plugins/issues/157

In summary, in Play 2.4.2, the current readme causes an exception to be thrown upon setting up @inject on JedisPool. The correct dependency is play-plugin-redis 2.4.1 (instead of 2.4.0).

Also, since all other dependencies need to participate in the dependency injection to obtain JedisPool via @Inject, I believe it is beneficial for new users to have this piece of information explicitly called out as part of the getting started step.

[lightbend-cla-validator]

Hi @ronaldwidha,

Thank you for your contribution! We really value the time you've taken to put this together.

Before we proceed with reviewing this pull request, please sign the Typesafe Contributors License Agreement:

http://www.typesafe.com/contribute/cla

[ronaldwidha]

I've signed the agreement.