Suggest full path for the `extends` key

[fregante]

You might not like this, but:

• this is the format suggested by TS’ docs: https://www.typescriptlang.org/docs/handbook/tsconfig-json.html#tsconfig-bases
• https://github.com/microsoft/vscode/issues/131643
  • (WebStorm does)

Feel free to close if unneeded though, I opened this here anyway because more editors might not support it. I spent years on TS unable to click the config and just now I figured out there was a way to make it work.