[Minor] Add some perf numbers to the readme or doc

## 🚀 Feature
Add some performance numbers to either the doc or the README (or a dedicated sub-README). That could apply to Pipe or ShardedOptimizer

## Motivation
People landing on this repo probably would love to know more about the practical implications

## Pitch
Just add 2 examples per technique for instance, baseline with caveats

## Alternatives
Not doing anything

## Additional context
cc @Vittorio-Caggiano

Start by locating the README or documentation sections for Pipe and ShardedOptimizer. Gather two practical performance examples per technique against a stated baseline, record caveats, and publish the results in the README, documentation, or a dedicated sub-README.

Written by the indexing model from the issue text.