fix(README): set installationId in code example (#350)

Co-authored-by: Gregor Martynus <39992+gr2m@users.noreply.github.com>

README.md

@@ -69,13 +69,16 @@ const app = new App({
 
 const { data } = await app.octokit.request("/app");
 console.log("authenticated as %s", data.name);
-
-for await (const { octokit, repository } of app.eachRepository.iterator()) {
-  await octokit.request("POST /repos/{owner}/{repo}/dispatches", {
-    owner: repository.owner.login,
-    repo: repository.name,
-    event_type: "my_event",
-  });
+for await (const { installation } of app.eachInstallation.iterator()) {
+  for await (const { octokit, repository } of app.eachRepository.iterator({
+    installationId: installation.id,
+  })) {
+    await octokit.request("POST /repos/{owner}/{repo}/dispatches", {
+      owner: repository.owner.login,
+      repo: repository.name,
+      event_type: "my_event",
+    });
+  }
 }
 
 app.webhooks.on("issues.opened", async ({ octokit, payload }) => {