Update docs

docs/migration.rst

@@ -1,8 +1,8 @@
 Schema Migrations
 ==================
 
-Datalite provides a module, ``datalite.migrations`` that handles schema migrations. When a class
-definition is modified, ``datalite.migrations.basic_migration`` can be called to automatically
+Datalite provides a module, ``aiodatalite.migrations`` that handles schema migrations. When a class
+definition is modified, ``aiodatalite.migrations.migrate`` can be called to
 transfer records to a table fitting the new definitions.
 
 Let us say we have made changes to the fields of a dataclass called ``Student`` and now,
@@ -13,7 +13,34 @@ name change. We can achieve this easily by:
 
 .. code-block:: python
 
-    datalite.basic_migration(Student, {'studentt_id': 'student_id'})
+    await migrate(Student, {'studentt_id': 'student_id'})
 
 This will make all the changes, if we had not provided the second argument,
-the values would be lost.
+the values would be lost.
+
+Also, ``migrate`` provides automatic backup before migration, you can turn it off by passing ``do_backup=False`` into
+function.
+
+We also introduce safe migration defaults. This parameter should be passed a key-value dictionary, where the key is the
+name of the new required field, and the value is what should be written to the old records in the database.
+
+.. code-block:: python
+
+    from aiodatalite import datalite
+    from aiodatalite.typed import DataliteHinted
+    @datalite(db_path='db.db')
+    @dataclass
+    class Student(DataliteHinted):
+        new_obligatory_field: str  # the database will break if not all records have this field
+        student_id: int = 1
+        student_name: str = "Kurt Gödel"
+        student_gpa: float = 3.9
+
+So in this situation basically what you need to do is:
+
+.. code-block:: python
+
+    await migrate(Student, safe_migration_defaults={
+            "new_obligatory_field": "some value for records that already exist in the database"
+        }
+    )