Add note about using additionalLftpCommands
Add note about using additionalLftpCommands

It wasn't clear and took me a while to figure out - so I added some notes for you.

I specified this for people experiencing the DH GEX group out of range issue. Thankfully this guy was along the right track: http://www.christophervickery.com/Notes/index.php/2016/10/21/dh_gex_group_out_of_range/

So I just had to figure out how to apply his fix to your library. I've been trying to find an sftp library all week which supports this since ssh2-streams cannot createReadStreams on legacy servers like the one I'm dealing with. [See Here](https://github.com/mscdex/ssh2-streams/issues/61)
Atinux/node-ftps