SHIBUI-2273

Readme for liquibase

backend/src/main/resources/db/changelog/README.txt

@@ -0,0 +1,18 @@
+Understanding the liquidbase changelog.sql file
+
+" -- liquibase formatted sql" - this is required at the top of this file "
+
+" -- changeset liquibase:1.11.0 dbms:mariadb,mysql,postgresql "
+This indicates a change set and the version - please use the release version that the change matches so that looking at the DB should
+give a good indication of what has been run.
+
+The dbms section indicates which DBs the changeset that follows is valid to be run on. If this is not present, Liquidbase will try
+to run the changeset always.
+
+" -- preconditions onFail:MARK_RAN "
+" -- precondition-sql-check expectedResult:1 SELECT count(*) FROM INFORMATION_SCHEMA.TABLES WHERE TABLE_NAME = N'users' "
+
+@see - https://docs.liquibase.com/concepts/changelogs/preconditions.html
+The check here is looking to see if the schema has been built out yet. If it has not, then the db is new and will be created
+correctly without needing to be updated, so MARK_RAN ensures that the given changeset will not be run, but will be added to the
+liquibase changesetlog table indicating that it was checked.