Add readme

Author: YuryHrytsuk

services/metabase/README.md

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+## How to deploy first time
+
+Before deploying metabase first time, make sure that postgres is configured:
+1. Generate SQL commands via `make configure_metabase.sql`
+2. Execute SQL commands from the script in psql shell
+    * you can get one via adminer or by directly connecting to container and executing `psql -U <user> -d <db>`
+
+This can be automated via https://github.com/ITISFoundation/osparc-ops-environments/issues/827