test images: Updates image building process README

Updates the README with the given suggestions.

Author: claudiubelu

test/images/README.md

@@ -15,13 +15,8 @@ In order to build the docker test images, a Linux node is required. The node wil
 and `docker (version 18.06.0 or newer)`. Manifest lists were introduced in 18.03.0, but 18.06.0
 is recommended in order to avoid certain issues.
 
-The node must be able to push the images to the desired container registry. Depending on the
-container registry, it might require a different authentication method. For dockerhub, this
-can be done by running the command:
-
-```bash
-    docker login -u your-awesome-username -p anAwesomerPassword
-```
+The node must be able to push the images to the desired container registry, make sure you are
+authenticated with the registry you're pushing to.
 
 
 ## Making changes to images
@@ -34,7 +29,7 @@ itself or its binaries will require the image's version to be bumped. In the cas
 which cannot be immediately resolved, the image version used in E2E tests will be reverted to the
 last known stable version.
 
-The version can easily be bumped by modifying the file `test/images/IMAGE_NAME/VERSION`, which will
+The version can easily be bumped by modifying the file `test/images/${IMAGE_NAME}/VERSION`, which will
 be used when building the image. Additionally, for the `agnhost` image, also bump the `Version` in
 `test/images/agnhost/agnhost.go`.
 
@@ -47,37 +42,47 @@ Some test images (`mounttest`, `test-webserver`) are used as bases for other ima
 `kitten`, `nautilus`). If the parent image's `VERSION` has been bumped, also bump the version in the
 children's `BASEIMAGE` files in order for base image changes to be reflected in the child images as well.
 
+TODO: Once [Centralization part 4](https://github.com/kubernetes/kubernetes/pull/81226) merges, the paragraph
+above will have to be updated, as those images will be included into `agnhost`.
+
+After the desired changes have been made, the affected images will have to be built and published,
+and then tested. After the pull request with those changes has been approved, the new images will be
+built and published to the `gcr.io/kubernetes-e2e-test-images` registry as well.
+
 
 ## Building images
 
 The images are built through `make`. Since some images (`mounttest`, `test-webserver`)
 are used as a base for other images, it is recommended to build them first, if needed.
 
+TODO: Once [Centralization part 4](https://github.com/kubernetes/kubernetes/pull/81226) merges, the paragraph
+above will have to be updated, as those images will be included into `agnhost`.
+
 An image can be built by simply running the command:
 
 ```bash
-    make all WHAT=test-webserver
+make all WHAT=test-webserver
 ```
 
 To build AND push an image, the following command can be used:
 
 ```bash
-    make all-push WHAT=test-webserver
+make all-push WHAT=test-webserver
 ```
 
 By default, the images will be tagged and pushed under the `gcr.io/kubernetes-e2e-test-images`
 registry. That can changed by running this command instead:
 
 ```bash
-    REGISTRY=foo_registry make all-push WHAT=test-webserver
+REGISTRY=foo_registry make all-push WHAT=test-webserver
 ```
 
 *NOTE* (for test `gcr.io` image publishers): Some tests (e.g.: `should serve a basic image on each replica with a private image`)
 require the `agnhost` image to be published in an authenticated repo as well:
 
 ```bash
-    REGISTRY=gcr.io/kubernetes-e2e-test-images make all-push WHAT=agnhost
-    REGISTRY=gcr.io/k8s-authenticated-test make all-push WHAT=agnhost
+REGISTRY=gcr.io/kubernetes-e2e-test-images make all-push WHAT=agnhost
+REGISTRY=gcr.io/k8s-authenticated-test make all-push WHAT=agnhost
 ```
 
 
@@ -88,7 +93,7 @@ by having the environment variable `KUBE_TEST_REPO_LIST` set before running the
 image:
 
 ```bash
-    export KUBE_TEST_REPO_LIST=/path/to/repo_list.yaml
+export KUBE_TEST_REPO_LIST=/path/to/repo_list.yaml
 ```
 
 `repo_list.yaml` is a configuration file used by the E2E tests, in which you can set alternative registries
@@ -106,12 +111,16 @@ Keep in mind that some tests are using multiple images, so it is a good idea to
 Finally, make sure to bump the image version used in E2E testing by modifying the file `test/utils/image/manifest.go`, and recompile afterwards:
 
 ```bash
-    ./build/run.sh make WHAT=test/e2e/e2e.test
+./build/run.sh make WHAT=test/e2e/e2e.test
 ```
 
 After all the above has been done, run the desired tests.
 
 
 ## Known issues and workarounds
 
-`docker manifest create` fails due to permission denied on `/etc/docker/certs.d/gcr.io` (https://github.com/docker/for-linux/issues/396)
+`docker manifest create` fails due to permission denied on `/etc/docker/certs.d/gcr.io` (https://github.com/docker/for-linux/issues/396). This issue can be resolved by running:
+
+```bash
+sudo chmod o+x /etc/docker
+```