docs: cleanup header levels in backend docs (#5698)

docs/content/sftp.md

@@ -29,6 +29,8 @@ directory for remote machine (i.e. `/`)
 good example of this. rsync.net, on the other hand, requires users to
 OMIT the leading /.
 
+## Configuration
+
 Here is an example of making an SFTP configuration.  First run
 
     rclone config
@@ -108,7 +110,7 @@ Mount the remote path `/srv/www-data/` to the local path
 
     rclone mount remote:/srv/www-data/ /mnt/www-data
 
-### SSH Authentication ###
+### SSH Authentication
 
 The SFTP remote supports three authentication methods:
 
@@ -562,7 +564,7 @@ Set to 0 to keep connections indefinitely.
 
 {{< rem autogenerated options stop >}}
 
-### Limitations ###
+## Limitations
 
 SFTP supports checksums if the same login has shell access and `md5sum`
 or `sha1sum` as well as `echo` are in the remote's PATH.