Add comment in conf/sonar.properties for Oracle installation

sonar-application/src/main/assembly/conf/sonar.properties

@@ -66,7 +66,9 @@ sonar.jdbc.driverClassName:                org.apache.derby.jdbc.ClientDriver
 
 
 #----- Oracle 10g/11g
-# Comment the embedded database and uncomment the following properties to use Oracle. The validation query is optional.
+# To use Oracle database :
+# - Copy the JDBC driver to extensions/jdbc-driver/oracle.
+# - Comment the embedded database and uncomment the following properties. The validation query is optional.
 #sonar.jdbc.url:                            jdbc:oracle:thin:@localhost/XE
 #sonar.jdbc.driverClassName:                oracle.jdbc.driver.OracleDriver
 #sonar.jdbc.validationQuery:                select 1 from dual