Change `books` to `movies` in README.md

[curquiza]

To keep the getting started simple to try, but to also make documentation examples compatible with the getting started, we are replacing book examples with movies examples.

The Movie dataset is used throughout the documentation. The only place where book is used is in the tests (which can stay as it is) and in our getting started.

Changes

• Index name should be changed in README.md

  const index = client.index('movies')

Provided dataset should be changed with the following:

 const documents = [
      { id: 1, title: 'Carol', genres: ['Romance', 'Drama'] },
      { id: 2, title: 'Wonder Woman', genres: ['Action', 'Adventure'] },
      { id: 3, title: 'Life of Pi', genres: ['Adventure', 'Drama'] },
      { id: 4, title: 'Mad Max: Fury Road', genres: ['Adventure', 'Science Fiction'] },
      { id: 5, title: 'Moana', genres: ['Fantasy', 'Action']},
      { id: 6, title: 'Philadelphia', genres: ['Drama'] },
  ]

• comment should be changed

// If the index 'movies' does not exist, MeiliSearch creates it when you first add the documents.

• All the other examples in the README should be updated accordingly

[The-Loony-Coder]

I would like to work on this issue.

[curquiza]

Go @The-Loony-Coder :D