update db_readme.txt to reflect properties rename

jdbc.properties was renamed to data-access.properties, but this file still referred to the old name.

src/main/resources/db_readme.txt

@@ -9,5 +9,5 @@
 In its default configuration, Petclinic uses an in-memory database (HSQLDB) which
 gets populated at startup with data. A similar setup is provided for Mysql in case
 a persistent database configuration is needed.
-Note that whenever the database type is changed, the jdbc.properties file needs to
-be updated.
\ No newline at end of file
+Note that whenever the database type is changed, the data-access.properties file needs to
+be updated.