Documentation (& code) regarding determining temp_storage_bytes not very clear about cccl

[daktfi]

From my experience with library, the arguments to calculate temp storage size are data type(s) (templated) and length of it.
I call the methods very early in the code with all pointers set to nullptr and only non-zero argument is size of the data to be processed and get the temp size that works fine till the very end.
Hope this helps.

[dumerrill]

Yep. That is the case for everything currently in CUB: we need to know the data types and length of input. The iterators:pointers can be null.

[alliepiper]

We should add a section to the docs about this. A generic section that explains the common pattern and conventions for using the cub::Device* API would be useful.