docs(Getting-Started): Install section only documents npm and yarn

Prerequisites

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Issue

The Install section of the Getting Started guide (docs/Guides/Getting-Started.md) documents only two package managers — npm i fastify and yarn add fastify.

Two of the most widely used package managers today, pnpm and bun, are missing. Because the guide enumerates package managers explicitly rather than saying "install it with your package manager of choice", the omission reads as "these are not supported" — which is exactly the impression that sent me looking.

Both work fine. Verified locally with bun 1.3.13:

$ bun add fastify
bun add v1.3.13
installed [email protected]
49 packages installed [1.65s]

A minimal server also boots and responds normally with that install.

To be explicit about scope: this is only about documenting how the package is installed with common package managers. It is not a request to treat Bun as a supported runtime — I'm aware of the project's position on that (see #5597).

Proposed change

Add two blocks to the Install section alongside the existing ones:

Install with pnpm:

pnpm add fastify

Install with bun:

bun add fastify

Happy to open a PR if this is welcome.