Add max_pages documentation to Readme
Add max_pages documentation to Readme

Recently ran into an issue where determining total_count for a collection created from a complex query was taking too long and timing out our server.  We didn't need to return all the records however, just a recent subset, so this method works perfectly and greatly reduces query time.  However we found no real documentation for this method and google searches proved mostly fruitless--wasn't until looking into the Kaminari codebase that I discovered this method could be applied per model.  I'd recommend adding some form of documentation to the readme to save future users the headache--feel free to use what I've provided here or substitute something else.  Thanks!
kaminari/kaminari,kaminari/kaminari