Make TypeScript ignore all other directories than e.g. `src/`

hint.md

TypeScript can have issues with with more folders containing TypeScript files than just the one used as rootDir, (e.g. migrations/ for Knex). (E.g. see this now archived/locked issue microsoft/TypeScript#9858).

The exclude option in tsconfig.json won't prevent this issue. Instead use the include option and include only the rootDir folder.

Example (showing only the relevant fields):

{
  "compilerOptions": {
    "rootDir": "./src"
  },
  "include": [
    "./src"
  ]
}