Restructure hosted contributor docs

Currently, contributor docs for lind-wasm and lind-wasm-docs structured like this:
```
├── Testing
│   └── Unit tests
└── More
    ├── Adding to the docs
    ├── Style guide
    └── GitHub Pull Request Guide (pending in #28)
```

I suggest a more coherent structure, like

```
└── Contribute
    ├── Setup Development Environment (TODO)
    ├── Test
    ├── Format
    ├── PR
    └── Docs
```