add docs

doc/db/user.mermaid

@@ -0,0 +1,41 @@
+classDiagram
+    class User {
+        +int id
+        +string name
+        +string pw
+        +bool deleted
+        +datetime last_access
+        +string dob
+        +string weight
+        +string sex
+        +string dirty_thirty
+        +string dirty_dozen
+        +string member_since_date
+        +string birthdate
+        +string mail
+        +string nickname
+        +string notes
+        +string phone
+        +string address
+        +int family_id
+        +blob membership_pdf
+        +string user_token
+    }
+
+    class Family {
+        +int id
+    }
+
+    class Role {
+        +int id
+        +string name
+    }
+
+    class UserRole {
+        +int user_id
+        +int role_id
+    }
+
+    User "1" -- "*" UserRole
+    Role "1" -- "*" UserRole
+    User "1" -- "0..1" Family