docs: auto generate backend options documentation

This inserts the output of "rclone help backend xxx" into the help
pages for each backend.

docs/content/box.md

@@ -217,8 +217,54 @@ normally 8MB so increasing `--transfers` will increase memory use.
 Depending on the enterprise settings for your user, the item will
 either be actually deleted from Box or moved to the trash.
 
-<!--- autogenerated options start - edit in backend/backend.go options  -->
-<!--- autogenerated options stop  -->
+<!--- autogenerated options start - DO NOT EDIT, instead edit fs.RegInfo in backend/box/box.go then run make backenddocs -->
+### Standard Options
+
+Here are the standard options specific to box (Box).
+
+#### --box-client-id
+
+Box App Client Id.
+Leave blank normally.
+
+- Config:      client_id
+- Env Var:     RCLONE_BOX_CLIENT_ID
+- Type:        string
+- Default:     ""
+
+#### --box-client-secret
+
+Box App Client Secret
+Leave blank normally.
+
+- Config:      client_secret
+- Env Var:     RCLONE_BOX_CLIENT_SECRET
+- Type:        string
+- Default:     ""
+
+### Advanced Options
+
+Here are the advanced options specific to box (Box).
+
+#### --box-upload-cutoff
+
+Cutoff for switching to multipart upload (>= 50MB).
+
+- Config:      upload_cutoff
+- Env Var:     RCLONE_BOX_UPLOAD_CUTOFF
+- Type:        SizeSuffix
+- Default:     50M
+
+#### --box-commit-retries
+
+Max number of times to try committing a multipart file.
+
+- Config:      commit_retries
+- Env Var:     RCLONE_BOX_COMMIT_RETRIES
+- Type:        int
+- Default:     100
+
+<!--- autogenerated options stop -->
 
 ### Limitations ###