I installed the Liferay IDE according to the following web site:
At the end of the instructions it says
Your runtime is now set up. Next, you need to register your Plugins SDK.
Select Window → Preferences → Liferay → Installed Plugin SDKs.
Click Add. Browse to the folder where you unzipped the Plugins SDK and click OK.
Click OK again.
But when I go to Windows -> Preferences -> Liferay, there is no Installed Plugin SDKs. Only the following:
Maven Plugin Validation XML Search