Added instruction on Dropzone javascript library

Author: libregeek

README.md

@@ -15,4 +15,8 @@ Installation Steps
 2. Rename the folder MantisBT-MarkDownEditor to MarkDownEditor
 3. Go to Manage-->Manage Plugins and install the plugin
 
+Known Issues
+------------
+It is not possible to report issues with attachments if the MarkDownEditor plugin is enabled. A workaround is to disable Dropzone in MantisBT by setting  `$g_dropzone_enabled = OFF;` in `config/config_inc.php`
+