Document how to get uploaded file name and content type

[23doors]

Filename and content type are saved as file buffer properties - filename and contentType.

E.g.

ctx.args.file.filename 
ctx.args.file.contentType

[Idered]

ctx.args.file.size would also be helpful

// Edit:

ctx.args.file.length is available

[mkucharz]

@mattlsp can you create some docs about how we are handling files in scripts?