Update contributing guide and dev env setup

you agree to license your contribution under the MIT License.  If you cannot

agree to this license, please do not open a pull request.

[MIT License]: https://minhee.mit-license.org/

[MIT License]: https://minhee.mit-license.org/2024/

### Development environment

Fedify uses [Deno] as the main development environment, and is tested with Deno,

[Node.js], and [Bun].  Therefore, you need to install Deno, Node.js, and Bun to

contribute to Fedify.

The recommended editor for Fedify is [Visual Studio Code] with

the [Deno extension] installed.  Or you can use any editor that supports Deno;

see the [*Set Up Your Environment* section][1] in the Deno manual.

> [!NOTE]

>

> Fedify heavily depends on code generation, so you need to run

> `deno task codegen` before coding or testing.

[Deno]: https://deno.com/

[Node.js]: https://nodejs.org/

[Bun]: https://bun.sh/

[Visual Studio Code]: https://code.visualstudio.com/

[Deno extension]: https://marketplace.visualstudio.com/items?itemName=denoland.vscode-deno

[1]: https://docs.deno.com/runtime/manual/getting_started/setup_your_environment/

### Coding conventions

~~~~ bash

deno fmt

deno task check

deno task test

deno task test-all

~~~~

### Docs

[inline links]: https://spec.commonmark.org/0.31.2/#inline-link

[setext headings]: https://spec.commonmark.org/0.31.2/#setext-headings

[ATX headings]: https://spec.commonmark.org/0.31.2/#atx-headings

[Bun]: https://bun.sh/

### Bug fix