improve helpText attributes

plugins/scm-git-plugin/src/main/resources/sonia/scm/git.config.js

@@ -37,6 +37,7 @@ registerConfigPanel({
     xtype: 'textfield',
     name: 'repositoryDirectory',
     fieldLabel: 'Repository directory',
+    helpText: 'The location of the Git repositories.',
     allowBlank : false
   }]
 });