[documentation] add `how to contribute` section to README

[FranciscoKloganB]

As a consumer of nuxt3-appwrite I want to be able to contribute to it spontanously So that the project may grow organically

Having an How to Contribute guide on the GitHub readme section is of the utmost important for OSS projects to survive and avoid premature deaths.

Something as simple as this might be enough (taken from nuxt/image) repository.

## Contributing

- Clone this repository
- Enable [Corepack](https://github.com/nodejs/corepack) using corepack enable
- Install dependencies using pnpm install
- Run pnpm dev:prepare to generate type stubs.
- Use pnpm dev to start [playground](https://github.com/nuxt/image/blob/main/playground) in development mode.

[YsarocK]

Hi Francisco!

Thanks for your message.

You're right, it's missing. Will add it tonight!

Have a good day, I wait for your PRs 😇

[FranciscoKloganB]

/bump