message: switch from typescript to diff syntax
  now it's proper syntax, based on suggestion.
diff: @@ -186,7 +186,7 @@ const app = createApp({
  In case you already have a dozen of internal ones, you may need to update those too.
  Assuming you follow the common plugin structure, the changes to your front-end may look like:
  -```typescript
  +```diff
  // plugins/internal-plugin/src/api.ts
  -- import {createApiRef} from '@backstage/core';
  ++ import {createApiRef, IdentityApi} from '@backstage/core';
  @@ -229,7 +229,7 @@ export class MyApi implements MyInterface {
  and
  -```typescript
  +```diff
  // plugins/internal-plugin/src/plugin.ts
  import {
  