Add new documentation for file uploads with Latch

[wout]

This resolves #1522.

Right now it's still referencing latch on my account but I'll update these guides once we move it to the Lucky org.

EDIT: I see I forgot to expand the line lengths. I tend to wrap at 80 characters, let me know if you prefer them to be unwrapped.

[jwoertink]

I'm ok with the 80 character limit. I usually do the same thing myself because it's easier for me to read.