docs: add permissions in readme

[Eomm]

Adding the permissions config.

New repos (or just me??) do not allow permessive github token:

So these permissions are necessary to avoid the error:

[Invalid workflow file: .github/workflows/ci.yml#L14](https://github.com/Eomm/fastify-telegram/actions/runs/6449305117/workflow)
The workflow is not valid. .github/workflows/ci.yml (Line: 14, Col: 3): Error calling workflow 'fastify/workflows/.github/workflows/plugins-ci.yml@v3'. The nested job 'automerge' is requesting 'contents: write, pull-requests: write', but is only allowed 'contents: read, pull-requests: none'.