History of FormData.append()

updated wording to match .set page

Previous text suggested you had to pass 3 args if the 2nd was not a string

Technical review completed.

Typo fix

Added an example that demonstrates the use of array notation in the first argument. This technique is helpful when dealing with multi-file uploads. I also corrected a broken hyperlink.

Fixed browser compatibility table to allow the compat data scraper to parse the page

Fixed specifications and removed translated tag

Editorial review