added Author class in models.py

bellapanghulan_reading/bookshelf/models.py

 from django.db import models
 
 # Create your models here.
+class Author(models.Model):
+    first_name = models.CharField(max_length = 50)
+    last_name = models.CharField(max_length = 50)
+    age = models.IntegerField(default = 0)
+    nationality = models.CharField(max_length = 50)
+    bio = models.TextField(max_length = 700)
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