[tutorial] edited hands-on practices (#1899)

* Add handson to ColossalAI.

* Change names of handsons and edit sequence parallel example.

* Edit wrong folder name

* resolve conflict

* delete readme

examples/tutorial/opt/zero/README.md

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+## Overview
+This example shows how to use ColossalAI to run huggingface GPT training with Gemini and ZeRO DDP.
+
+## GPT
+We use the huggingface transformers GPT2 model. The input data is randonly generated.
+
+## Our Modifications
+We adapt the OPT training code to ColossalAI by leveraging Gemini and ZeRO DDP.
+
+## Quick Start
+You can launch training by using the following bash script
+
+```bash
+pip install -r requirements.txt
+bash run.sh
+```