Add doc for public tensor operation

I noticed that lots public tensor operation miss related document, such as https://docs.rs/candle-core/latest/candle_core/struct.Tensor.html#method.scatter_set . It maybe worth to add example document fot them to clear semantics of each operation.

Start with the linked Tensor::scatter_set documentation on docs.rs and inspect the public tensor operations around it. Identify which operations lack examples and add documentation that clarifies their semantics; done means the selected public operations have useful examples.

Written by the indexing model from the issue text.