Imrpoved docstring for np.tensordot()

I feel that the docstring for `np.tensordot()` may be more explicit so users can find words of "tensor product" and "tensor contraction" directly by doing a search. Any comments are welcome.
The function argument handling is perhaps over general. It might be clearer to just document `int` and `tuple` for the axes argument, although more general forms are accepted. So maybe something like
```
    axes : {int, tuple}
        * int N
             Sum over the last N axes of `a` and the first N axes of `b`. The size of the corresponding axes must match.
        ...
```