new read methods

[jimmywarting]

new blobs already have a promise api - it should be recommended/mention that it's now possible to do

• await blob.text()
• await blob.arrayBuffer()
• blob.stream()
• await new Response(blob).json()
• img.src = URL.createObjectURL(blob) cuz you don't need base64 dataUrl

and using the filereader is discouraged since NodeJS have buffer.Blob but no FileReader for example.