backups.md: Add mention of Yearly backups

Signed-off-by: Thomas Moraine <[email protected]>

docs/docs/backups.md

@@ -401,9 +401,10 @@ To enable GFS retention:
 3. Click the **Delta Backup** button.\
 The section called **Long-term retention of backups** appears.
 4. In that section, you can define the following:
-- **Daily backups** (Son): The number of daily backups to keep.
-- **Weekly backups** (Father): The number of weekly backups to keep.
-- **Monthly backups** (Grandfather): The number of monthly backups to keep.
+- **Daily backups**: The number of daily backups to keep.
+- **Weekly backups** (Son): The number of weekly backups to keep.
+- **Monthly backups** (Father): The number of monthly backups to keep.
+- **Yearly backups** (Grandfather): The number of monthly backups to keep.
 5. Click the **Save** button.
 
 During each backup run, Xen Orchestra evaluates existing backups and removes any excess backups based on the configured policy.