style: fix markdown linting issue

Author: weyert

packages/opentelemetry-resource-detector-gcp/README.md

@@ -19,7 +19,7 @@ npm install --save @opentelemetry/resource-detector-gcp
 
 ## Usage
 
-```
+```typescript
 import { detectResources } from '@opentelemetry/resources';
 import { gcpDetector } from '@opentelemetry/resource-detector-gcp'
 const resource = await detectResources({