title: django adding values to foerignkey field
body: <p>I have a simple application which requires each employee can have multiple files, so i created two models one is Employee and the other one is Files</p>
  
  <pre><code>class Files(models.Model):
      files = models.FileField(upload_to='files')
  
  class Employee(models.Model):
      name = models.CharField(max_length=200)
      email = models.EmailField()
      cv = models.ForeignKey(
          Files, on_delete=models.CASCADE)
  </code></pre>
  
  <p>when i try to upload a file it gives me an error.</p>
  
  <pre><code>Cannot assign "'list-employees.png'": "Employee.cv" must be a "Files" instance.
  
  Exception Type:     ValueError
  </code></pre>