[Doc] Enhance the document's structure

[sun7927]

Suggested the new structure of document as below:

1. What's the HwameiStor
2. Quick Start
   2.1 Installations
   2.2 Start a Stateful Application
   2.2.1 Basic Operations
   2.2.2 Advanced Operations
   2.3 Advanced Features
   2.3.1 Node Expansion
   2.3.2 Disk Expansion
   2.3.3 Upgrade
   2.4 Uninstall
3. Architecture of HwameiStor
   3.1 Overview
   3.2 Components
   3.3 Resources
   3.4 APIs
4. Development Designs (Optional)
5. Applications
   5.1 TiDB
   5.2 MinIO
   ...
6. Terminologies
7. Community
8. FAQs

[alexzhc]

working on a doc pr.