Add lazy loading instructions to readme

[goelinsights]

Not sure what current best practices are but would be great to see ngrx setup instructions in the readme updated to fit with the AoT lazy loading modules approach...found it as a closed issue but would be much more helpful in the readme to better map to angular style guide

I've been pulling from @MikeRyan52 example: #197

[robwormald]

Implemented and released in v4.