btrfs-progs: ci: update documentation

Write a quick start howto and point to the admin scripts.

Signed-off-by: David Sterba <dsterba@suse.com>

ci/README.md

@@ -5,6 +5,18 @@ functionality is in user space and does not need a virtual machine. The
 features supported by the running kernel are detected and tests skipped
 eventually.
 
+## Quick start
+
+- install docker, add `"storage-driver": "btrfs"` to */etc/docker/daemon.json*,
+  make sure your user is in group *docker*, start the service
+- pull all images by `ci/images/images-base-update`, this can take time
+- build all images for testing by `ci/images/images-build-all`, or individually
+  in the *ci/images/ci-\** directories
+- build current branch and test it in the docker image by running `ci/ci-build-musl` from
+  the top directory (this will create a fresh tar archive inside the docker sources
+  and the image must be rebuilt)
+- `ci/ci-build-*` scripts to build on the target image
+
 ## Hosted
 
 No active hosted CI is currently set up, we're looking for one.
@@ -135,8 +147,21 @@ image template or enhancing current support scripts.
 To do:
 
 - 32bit coverage -- while this architecture is fading out, it may be useful to
-  still have some coverage, however running 32bit docker in 64bit is not
-  considered experimental does not work out of the box
+  still have some coverage, however running 32bit docker in 64bit is
+  considered experimental and does not work out of the box
 - add some kind of templates, there's a lot of repeated stuff in the
   *Dockerfile*s and the scripts need to be inside the directories in order to
   allow copying them to the image
+
+## Administration
+
+To pull all base images from docker hub or to update already downloaded ones run
+
+    ci/images/images-base-update
+
+Before running the CI tests locally the images need to be build from the templates,
+for that there's
+
+    ci/images/images-build-all
+
+Which is similar to running the `docker-build` command inside the directories.