fix(doc): Add "compilerOptions" to bun-types README.md

[philolo1]

What does this PR do?

This updates the documentation for how to add bun-types.
Reading the documentation on bun-types it was not clear to me that the tsconfig.ts needs to look like this:

{
  "compilerOptions": {
    "types": ["bun-types"]
  }
}

So i added the "compilerOptions" information.

• [ x ] Documentation or TypeScript types (it's okay to leave the rest blank in this case)

How did you verify your code works?

• [ x ] Checked the readme on my pr

[colinhacks]

Thanks!