README examples don't reflect proper usage

[stkrzysiak]

The readme gives the following example:

a := New(WithShape(2, 2), WithBacking([]int{1, 2, 3, 4}))
fmt.Printf("a:\n%v\n", a)

I think this should be:

a := tensor.New(tensor.WithShape(2, 2), tensor.WithBacking([]int{1, 2, 3, 4}))
fmt.Printf("a:\n%v\n", a)

This is how gorgonia uses it currently.
I think the readme was probably using dot imports where the package name wasn't necessary but it is not recommended to do that.

Dot imports. If a program imports a standard package using import . "path", additional names defined in the imported package in future releases may conflict with other names defined in the program. We do not recommend the use of import . outside of tests, and using it may cause a program to fail to compile in future releases.

[yati-sagade]

As a new Go user, I also ran into this. But I appreciate the reduced clutter with the current style. Maybe the docs could just mention the import statement one needs at the top, and then assume the user adds the package prefix thereafter?