add migration url to deprecation message of paramsHelp

plugins/nf-schema/src/main/nextflow/validation/SchemaValidator.groovy

@@ -369,7 +369,7 @@ class SchemaValidator extends PluginExtensionPoint {
         // TODO add link to help message migration guide once created
         if (!options.containsKey("hideWarning") || options.hideWarning == false) {
             log.warn("""
-Using `paramsHelp()` is not recommended. Check out the help message migration guide: <url>
+Using `paramsHelp()` is not recommended. Check out the help message migration guide: https://nextflow-io.github.io/nf-schema/latest/migration_guide/#updating-the-help-message
 If you intended to use this function, please add the following option to the input of the function:
     `hideWarning: true`