docs: add note about test-images quay repo

docs/Installation.md

@@ -91,7 +91,7 @@ are in the [infra-deployments](https://github.com/redhat-appstudio/infra-deploym
 
 Most of the tests could require you to have specific container image repo's created (if you're using your own container image org/user account (`QUAY_E2E_ORGANIZATION`) or your own GitHub organization (`MY_GITHUB_ORG`).
 In that case, before you run the test, make sure you have created
-* `test-images` repo in quay.io, i.e. `quay.io/<QUAY_E2E_ORGANIZATION>/test-images` and make it **public**
+* `test-images` repo in quay.io, i.e. `quay.io/<QUAY_E2E_ORGANIZATION>/test-images` and make it **public** (this repo will be used for pushing container images produced by tests)
   * also make sure that the docker config, that is encoded in the value of `QUAY_TOKEN` environment variable, contains a correct credentials required to push to `test-images` repo. And make sure the robot account or user account has the **write** permissions set for `test-images` repo which is required by the tests to push the generated artifacts.
 * fork following GitHub repositories to your org (specified in `MY_GITHUB_ORG` env var)
   * https://github.com/redhat-appstudio-qe/devfile-sample-hello-world (for running build-service tests)