DOCS: Add the configurable settings to the Readme/VSCode doc

[DiarmuidKelly]

In here: https://github.com/bufbuild/vscode-buf/blob/main/package.json#L132 you are injecting default settings.

These are not that easy to find:

settings.json:

{
  "buf.binaryPath": "/path/to/buf",
  "[proto]": {
    "editor.formatOnSave": false,
    "editor.defaultFormatter": null
  }
}

and there are no instructions on settings.json configs

[stefanvanburen]

hey @DiarmuidKelly; agreed that we could mention formatOnSave (similar to vscode-go, which mentions it in it's README). Do you really need to unset defaultFormatter if you're already disabling formatting on save? And I'm not sure if buf.binaryPath is still a valid setting, unless that's a general VS Code thing?