So, you've created some custom icons that you think would be useful to other users? You can add those icons to your organization library to make them available to your colleagues.
If you do not have administrative access, skip down to the When you do not have administrative access section below. Otherwise, continue on...
When you have administrative access
If you do have administrative access, you can add an icon directly to the organization library while you are in a project. First, make sure that you have the organization library enabled.
Once you ensure you have the organization library enabled, you can click any icon (NOTE: this does not yet work for icon bundles) in any library that you have available and click the Copy button shown at the bottom of the library.
That will pop up a dialog allowing you to make any changes to the icon that might be necessary. On the last step of that dialog, you should see a Save to... button. Click that to get a dropdown allowing you to choose the library you save it to. Finally, click on the name of your organization to save it to the organization library, making it available to everyone else on your team. If you do not see the name of your organization, you likely did not enable the organization library on your account.
When you do not have administrative access
If you do not have administrative access, then you need to use the promotion process to add your personal icons to the organization library. Simply click on the icon that you would like to have promoted and click the Promote button found at the bottom of the library.
A promotion request will be sent to your team members that have administrative access and they will be able to approve the icon, adding it to the organization's library.