Update database setup guide and introduce password for DB connection

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