chg: doc: [rocketchat] instruction for test and prepare new release

Signed-off-by: Valentin Lab <valentin.lab@kalysto.org>

rocketchat/README.org

@@ -6,33 +6,55 @@
 
 * Updating the charm to a new version
 
-We are using official image. Latest tags usually. You can
-double-check available candidate for official images like this:
+We are using official image. Latest tags usually.
 
-#+begin_src sh
-docker search rocket.chat
-#+end_src
+** Test new version
+
+Rocket.chat has a powerfull and working database update mecanism that
+will take care of migrating database on startup.
 
-So we usually pull and test images like this :
+*** Get latest available versions
+
+You can double-check available candidate for official images like this:
 
 #+begin_src sh
-docker pull rocket.chat:X.Y.Z
+docker-tags-fetch rocketchat/rocket.chat -l 15 -f "^[0-9]+\.[0-9]+\.[0-9]+$" | sort -rV
 #+end_src
 
-This worked on 3.6.3, but changed before 3.8.0 to:
+Check/Choose the version you want to test.
 
-#+begin_src sh
-docker pull rocketchat/rocket.chat:X.Y.Z
+*** Modify your own =compose.yml=
+
+By adding these 2 lines in your rocket chat service:
+
+#+begin_src yaml
+  docker-compose:
+    image: rocketchat/rocket.chat:X.Y.Z
 #+end_src
 
-from: https://hub.docker.com/r/rocketchat/rocket.chat
+Replace X.Y.Z by the target version you want to test.
+
+Launch =compose up=.
+
+Be ready to wait a few minutes after =compose up= finished before the
+service to be available: rocketchat is expected to take some time to
+migrate.
 
-Get the available tags:
+
+** Change the current charm to include new version
+
+To prepare the commit for next version, you can run the following
+on the repository you'll use to push the new commit.
 
 #+begin_src sh
-docker-tags-fetch rocket.chat -l 15 -f "^[0-9]+\.[0-9]+\.[0-9]+" | sort -V
+BASENAME=rocketchat/rocket.chat
+VERSION=$(docker-tags-fetch "$BASENAME" -l 15 -f "^[0-9]+\.[0-9]+\.[0-9]+$" | sort -rV | head -n 1)
+echo Last version of rocket chat: $VERSION
+docker pull rocketchat/rocket.chat:"$VERSION" &&
+docker tag rocketchat/rocket.chat:"$VERSION" docker.0k.io/rocketchat:"$VERSION" &&
+docker push docker.0k.io/rocketchat:"$VERSION" &&
+sed -ri "s%^(docker-image: docker.0k.io/rocketchat:).*%\1$VERSION%" metadata.yml &&
+sed -ri "s%^(#docker-image: rocketchat/rocket.chat:).*%\1$VERSION%" metadata.yml
 #+end_src
 
-Rocket.chat has a powerfull and working update database that will
-take care of migrating database on startup.
-
+You can review the changes and commit them.