[ao][sparsity] README for data sparsifier benchmarking (#81781)
The README contains the results of the benchmarking exercise and area of future work.
It also contains instructions to run the benchmarking scripts to reproduce the results.
Also, contains other information such as requirements, machine config etc.
Test Plan: None
Pull Request resolved: https://github.com/pytorch/pytorch/pull/81781
Approved by: https://github.com/z-a-f
