[Documentation] Document user-db

documentation/databases.md

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+# Databases
+
+Oodikone uses three separate databases, each for different purposes. This document contains a simplified overview of each database.
+
+Please note that each database may contain additional information such as migration tables or indices that are not depicted here. For more details, inspect the actual databases via the commandline.
+
+## user-db
+
+The `user-db` database contains information about users of Oodikone.
+
+```mermaid
+erDiagram
+  users {
+    bigint         id              PK "not null"
+    varchar(255)   full_name
+    varchar(255)   username        UK
+    varchar(255)   language           "default: 'fi'"
+    varchar(255)   email
+    varchar(255)   sisu_person_id
+    timestamp      last_login
+    varchar(255)[] roles              "not null, default: []"
+    varchar(255)[] programme_rights   "not null, default: []"
+  }
+```