Hello World example/'vscode-graphql.contentProvider' failed

I'm probably doing something very basic wrong, as I'm just learning GraphQL.

In VS Code, I created a **`.gql` file** with the following contents:

```gql
POST https://api.github.com/graphql
Authorization: bearer ghp_my0token0here

query($owner:String!, $name:String!) {
repository(owner: $owner, name: $name) {
url, stargazerCount
}
}
```

Then I run **"Execute GraphQL Operations"** via the Command Palette and receive the following error:

> Running the contributed command: 'vscode-graphql.contentProvider' failed.

As said above, I'm probably doing something very basic wrong, but IMO this error message is not descriptive at all. Maybe you could give me a short hint what I am expected to do instead in order to test out my query from VS Code? :-)