docs: add GQLoom integration documentation

[xcfox]

Hello!

I am the maintainer of GQLoom.

GQLoom is a new GraphQL Schema producer. Unlike traditional Schema Builders, GQLoom doesn't have a built-in Builder API. Instead, it leverages popular schema libraries like Zod, Valibot, Yup, Effect Schema, or ORM entities/models like Prisma, Drizzle, MikroORM.

GQLoom provides first-class type safety, minimal boilerplate code, ergonomic API design, and an easy learning curve.

A simple example is as follows:

import { resolver, query, weave } from "@gqloom/core"
import { ZodWeaver } from "@gqloom/zod"
import { zod } from "zod"

const helloResolver = resolver({
  hello: query(z.string())
    .input({ name: z.string().nullish() })
    .resolve(({ name }) => `Hello, ${name ?? "World"}!`),
})

export const schema = weave(ZodWeaver, helloResolver)

Or using valibot:

import { resolver, query, weave } from "@gqloom/core"
import { ValibotWeaver } from "@gqloom/valibot"
import * as v from "valibot"

const helloResolver = resolver({
  hello: query(v.string())
    .input({ name: v.nullish(v.string(), "World") })
    .resolve(({ name }) => `Hello, ${name}!`),
})

export const schema = weave(ValibotWeaver, helloResolver)

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This PR adds comprehensive documentation for integrating GQLoom with Mercurius.