feat: add download progress example

[AuHau]

No description provided.

[vojtechsimetka]

@AuHau I see the header decompressed-content-length does not work without CORS disabled. It is not listed in the e.target.getAllResponseHeaders() and if I try to access it browser complains with Refused to get unsafe header "decompressed-content-length". It took me quite some time to figure this out, maybe we should document this in readme, hmm? :)

[vojtechsimetka]

Suggested change

	<div id="content">
	<div id="logs">

[vojtechsimetka]

This is an assignment to private variable.

Suggested change

	e.total = e.target.getResponseHeader('decompressed-content-length')
	progressCb(e)
	progressCb({...e, total: e.target.getResponseHeader('decompressed-content-length')})