Fix error in --stream example

[ajasmin]

The manual contains an error in regard to --stream

[[],"a",["b"]] becomes [[0],[]], [[1],"a"], and [[1,0],"b"].

This PR fix the last value to be [[2,0],"b"] (wrong index)

This is in fact followed by [[2,0]] and [[2]]. We should also mention this and explain why that is.

[coveralls]

Coverage remained the same at 84.134% when pulling 38b3193 on ajasmin:master into a17dd32 on stedolan:master.

[ajasmin]

already fixed by #2010