Update database setup guide and introduce password for DB connection

doc/README

@@ -23,8 +23,14 @@
     ------------------
     First install PostgreSQL. Then create a user for financer:
         sudo -iu postgres
-        createuser --interactive
+        createuser -P -s -e financer
-    Enter 'financer' as role name and make it superuser. Then create the actual database:
+    This creates a user named 'financer' and prompts for the creation of a password for this user. The expected default
+    password is 'financer'. Then create the actual database:
         createdb financer
-    Naming both, the user and the database, 'financer' is the expected default. If you want any other names you need
+    Using 'financer' for the name of the user, its password and the database name is the expected default. If you want
-    to adjust the database connection settings of the financer application.
+    any other values you need to adjust the database connection settings of the financer application.
+    Then you need to grant the created user permission to the created database:
+        psql
+        GRANT ALL PRIVILEGES ON DATABASE "financer" to financer;
+        \q
+        exit

src/main/resources/config/application-postgres.properties

@@ -2,6 +2,7 @@ spring.flyway.locations=classpath:/database/postgres,classpath:/database/common
 
 spring.datasource.url=jdbc:postgresql://localhost/financer
 spring.datasource.username=financer
+spring.datasource.password=financer
 
 # See https://github.com/spring-projects/spring-boot/issues/12007
 spring.jpa.properties.hibernate.jdbc.lob.non_contextual_creation=true