Merge pull request #12711 from ggouzi/doc-delete-image

doc: Add paragraph on how to delete images

doc/howto/images_manage.md

@@ -67,6 +67,17 @@ To edit the full image properties, including the top-level properties, enter the
 
     lxc image edit <image_ID>
 
+## Delete an image
+
+To delete a local copy of an image, enter the following command:
+
+    lxc image delete <image_ID>
+
+Deleting an image won't affect running instances that are already using it, but it will remove the image locally.
+
+After deletion, if the image was downloaded from a remote server, it will be removed from local cache and downloaded again on next use.
+However, if the image was manually created (not cached), the image will be deleted.
+
 ## Configure image aliases
 
 Configuring an alias for an image can be useful to make it easier to refer to an image, since remembering an alias is usually easier than remembering a fingerprint.