The JIRA gadget directory displays all the gadgets that are available for JIRA users to add to their dashboard.
You need to have administrator privileges to add a gadget to the directory. If you have permission to add gadgets to and remove gadgets from the directory itself, you will see the 'Add Gadget to Directory' and 'Remove' buttons on the 'Add Gadget' screen, as shown below.
Instead, you will need to follow the instructions for adding a plugin, as described in Managing JIRA's Plugins.
Once you have installed your plugin, the gadget will automatically appear in the directory.