message: update rollbar backend readme
diff: @@ -4,6 +4,57 @@ Simple plugin that proxies requests to the [Rollbar](https://rollbar.com) API.
  ## Setup
  +1. Install the plugin using:
  +
  +```bash
  +# From your Backstage root directory
  +yarn add --cwd packages/backend @backstage/plugin-rollbar-backend
  +```
  +
  +2. Create a `rollbar.ts` file inside `packages/backend/src/plugins/`:
  +
  +```typescript
  +import { createRouter } from '@backstage/plugin-rollbar-backend';
  +import { Router } from 'express';
  +import { PluginEnvironment } from '../types';
  +
  +export default async function createPlugin(
  + env: PluginEnvironment,
  +): Promise<Router> {
  + return await createRouter({
  + logger: env.logger,
  + config: env.config
  + });
  +}
  +```
  +
  +3. Modify your `packages/backend/src/index.ts` to include:
  +```diff
  + ...
  +
  + import { Config } from '@backstage/config';
  + import app from './plugins/app';
  ++import rollbar from './plugins/rollbar';
  + import scaffolder from './plugins/scaffolder';
  +
  + ...
  +
  + async function main() {
  +
  + ...
  +
  + const authEnv = useHotMemoize(module, () => createEnv('auth'));
  ++ const rollbarEnv = useHotMemoize(module, () => createEnv('rollbar'));
  + const proxyEnv = useHotMemoize(module, () => createEnv('proxy'));
  +
  + ...
  +
  + const apiRouter = Router();
  + apiRouter.use('/catalog', await catalog(catalogEnv));
  ++ apiRouter.use('/rollbar', await rollbar(rollbarEnv));
  + apiRouter.use('/scaffolder', await scaffolder(scaffolderEnv));
  +```
  +
  The following values are read from the configuration file.
  ```yaml
  