Added a maintaince README.

MAINT.md

@@ -0,0 +1,23 @@
+## For Project Maintainer: How to update seafile-docker when a new version is released
+
+Imagine the previous version is 6.0.5 and we have released 6.0.7. Here are the steps to do the upgrade.
+
+* Switch to a branch "unstable"
+```sh
+git branch -f unstable origin/master
+git checkout unstable
+```
+* Update the version number in all the files/scripts from "6.0.5" to "6.0.7" and push it to github, then wait for travis ci (https://travis-ci.org/haiwen/seafile-docker/builds) to pass
+```sh
+git push origin unstable:unstable
+```
+* Create a tag "v6.0.7" and push it to github. Wait for travis ci to finish: this time it would push the image seafileorg/server:6.0.7 to docker hub since it's triggered by a tag.
+```sh
+git tag v6.0.7
+git push origin v6.0.7
+```
+* Ensure the new image is available in https://hub.docker.com/r/seafileorg/server/tags/
+* Now update the master branch.
+```
+git push origin unstable:master
+```

ci/ci.sh

@@ -21,4 +21,6 @@ sudo ./launcher -v rebuild --docker-args "--memory 1g"
 
 if [[ $TRAVIS_TAG != "" ]]; then
     ci/publish-image.sh
+else
+    echo "Not going to push the image to docker hub, since it's not a build triggered by a tag"
 fi