Just found this link that will download a comprehensive Litchi "Software Manual" in pdf format. The link is dated Feb. 14, 2020.
NOTE: Link works inconsistently.I had to try several times to get a valid download using Firefox. Or you can paste "unlocking the full potential of your dji aircraft with litchi" into Google Go and select the pdf link. YMMV ?
Unlocking the full potential of your DJI aircraft with Litchi"