title: Add fields to entity by means of jhipster
body: <p>I created entity with help jhipster and modify entity manually.
  Over time I need to add more field. 
  I run <code>jhipster entity Download</code> and follow instructions step-by-step. Thereafter generator say about conflicts and offers to completely replace many files:</p>
  
  <pre><code> conflict .jhipster/Download.json
  ? Overwrite .jhipster/Download.json? show the differences between the old and the new
  </code></pre>
  
  <p>So it should be?
  Then I do not understand for what code contains next comment lines:</p>
  
  <pre><code>@CreatedBy
  @ManyToOne
  @JsonIgnoreProperties("downloads")
  private User user;
  
  // jhipster-needle-entity-add-field - JHipster will add fields here, do not remove
  public UUID getId() {
      return id;
  }
  </code></pre>