Add documentation about dropping a column in multiple steps

docs/incompatibilities.md

@@ -109,7 +109,9 @@ Deletion operations often lead to errors during deployment.
 4. restore a backup  of your data (if available and fresh enough)
 
 :white_check_mark: **Solutions**:
-- Deprecate the column before dropping it using [django-deprecate-fields](https://github.com/3YOURMIND/django-deprecate-fields/)
+- Deprecate the column before dropping it using [django-deprecate-fields](https://github.com/3YOURMIND/django-deprecate-fields/).
+This process requires to first make sure that the field is unused (for which `django-deprecate-fields` is made for).
+Once the column is unsed, drop it in a migration. This migration will require to be ignored through the [IgnoreMigration](docs/usage.md#ignoring-migrations) for instance.
 - Don't actually drop the column, but fake the drop migration until you are sure you won't roll back.
 Be careful :warning: fake dropping a non-nullable column without a database default will create errors once the code is not aware of the column anymore.
 
@@ -127,7 +129,7 @@ Be careful :warning: fake dropping a non-nullable column without a database defa
 4. restore a backup  of your data (if available and fresh enough)
 
 :white_check_mark: **Solutions**:
-- Do a multistep deleting. First, only update the code to make sure it is not querying the table anymore
+- Do a multistep deletion. First, only update the code to make sure it is not querying the table anymore
 
 ### :arrow_forward: Altering a column