This is strange, since the support for these annotations is one of the main unique features.
Note that the inspection settings does contain a relevant checkbox.

However, I think that the description itself should mention this as well, for two reasons:

• Most users will access the description using Ctrl-F1, and would expect to find something relevant there
• Searching for "@NotNull" in the inspections dialog doesn't find this inspection. Instead, the "@Nullable/@NotNull problems" inspection is found.

I think the overall situation is quite confusing for new users that want to try the @NotNull support.