Update examples/cloud-sql-mysql/main.tf

Add github address

Co-Authored-By: autero1 <petri.autero@gmail.com>

examples/cloud-sql-mysql/main.tf

@@ -10,6 +10,9 @@ terraform {
 }
 
 module "mysql" {
+  # When using these modules in your own templates, you will need to use a Git URL with a ref attribute that pins you
+  # to a specific version of the modules, such as the following example:
+  # source = "git::git@github.com:gruntwork-io/terraform-google-sql.git//modules/mysql?ref=v0.1.0"
   source           = "../../modules/mysql"
 
   project = "${var.project}"