(it's the "Superstore" marked in blue on the map on that page. Aldgate
East is off to the left along the green road. It shouldn't be more
than 10-15 minutes walk.
If you want a really big, cheap supermarket, get the 135 to
Crossharbour Asda, also shown on the bus map. There are also a several
convenience stores and a market outside Whitechapel station. I don't
think there are many shops around Aldgate East.