docs: auto generate backend options documentation

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

docs/content/sftp.md

@@ -158,8 +158,126 @@ upload (for example, certain configurations of ProFTPd with mod_sftp). If you
 are using one of these servers, you can set the option `set_modtime = false` in
 your RClone backend configuration to disable this behaviour.
 
-<!--- autogenerated options start - edit in backend/backend.go options  -->
-<!--- autogenerated options stop  -->
+<!--- autogenerated options start - DO NOT EDIT, instead edit fs.RegInfo in backend/sftp/sftp.go then run make backenddocs -->
+### Standard Options
+
+Here are the standard options specific to sftp (SSH/SFTP Connection).
+
+#### --sftp-host
+
+SSH host to connect to
+
+- Config:      host
+- Env Var:     RCLONE_SFTP_HOST
+- Type:        string
+- Default:     ""
+- Examples:
+    - "example.com"
+        - Connect to example.com
+
+#### --sftp-user
+
+SSH username, leave blank for current username, ncw
+
+- Config:      user
+- Env Var:     RCLONE_SFTP_USER
+- Type:        string
+- Default:     ""
+
+#### --sftp-port
+
+SSH port, leave blank to use default (22)
+
+- Config:      port
+- Env Var:     RCLONE_SFTP_PORT
+- Type:        string
+- Default:     ""
+
+#### --sftp-pass
+
+SSH password, leave blank to use ssh-agent.
+
+- Config:      pass
+- Env Var:     RCLONE_SFTP_PASS
+- Type:        string
+- Default:     ""
+
+#### --sftp-key-file
+
+Path to unencrypted PEM-encoded private key file, leave blank to use ssh-agent.
+
+- Config:      key_file
+- Env Var:     RCLONE_SFTP_KEY_FILE
+- Type:        string
+- Default:     ""
+
+#### --sftp-use-insecure-cipher
+
+Enable the use of the aes128-cbc cipher. This cipher is insecure and may allow plaintext data to be recovered by an attacker.
+
+- Config:      use_insecure_cipher
+- Env Var:     RCLONE_SFTP_USE_INSECURE_CIPHER
+- Type:        bool
+- Default:     false
+- Examples:
+    - "false"
+        - Use default Cipher list.
+    - "true"
+        - Enables the use of the aes128-cbc cipher.
+
+#### --sftp-disable-hashcheck
+
+Disable the execution of SSH commands to determine if remote file hashing is available.
+Leave blank or set to false to enable hashing (recommended), set to true to disable hashing.
+
+- Config:      disable_hashcheck
+- Env Var:     RCLONE_SFTP_DISABLE_HASHCHECK
+- Type:        bool
+- Default:     false
+
+### Advanced Options
+
+Here are the advanced options specific to sftp (SSH/SFTP Connection).
+
+#### --sftp-ask-password
+
+Allow asking for SFTP password when needed.
+
+- Config:      ask_password
+- Env Var:     RCLONE_SFTP_ASK_PASSWORD
+- Type:        bool
+- Default:     false
+
+#### --sftp-path-override
+
+Override path used by SSH connection.
+
+This allows checksum calculation when SFTP and SSH paths are
+different. This issue affects among others Synology NAS boxes.
+
+Shared folders can be found in directories representing volumes
+
+    rclone sync /home/local/directory remote:/directory --ssh-path-override /volume2/directory
+
+Home directory can be found in a shared folder called "home"
+
+    rclone sync /home/local/directory remote:/home/directory --ssh-path-override /volume1/homes/USER/directory
+
+- Config:      path_override
+- Env Var:     RCLONE_SFTP_PATH_OVERRIDE
+- Type:        string
+- Default:     ""
+
+#### --sftp-set-modtime
+
+Set the modified time on the remote if set.
+
+- Config:      set_modtime
+- Env Var:     RCLONE_SFTP_SET_MODTIME
+- Type:        bool
+- Default:     true
+
+<!--- autogenerated options stop -->
 
 ### Limitations ###