Add DDP training README

Add Sth-Sth-v2 Preprocessing & XLA Pretraining Script (#10)

* Update xpretrain documentation

* Update README

* Add Sth-Sth-v2 Preprocessing Pipeline

* Add model initialization stub

* Add full XLA pretraining pipeline

* Add v1.0.0 with full preprocessing/XLA pretraining pipeline

Voltron-Robotics 0.0.1 Release