Windows 7 End of Life (KB4493132)
You should know - if you do not - that Microsoft will end Windows 7 support in January 2020.
Specifically, no further patches or updates will be released after January 20th, 2020. Your computer will continue to run but any new issues found will not be patched. Also, over time, other applications will eventually drop support for Windows 7. This varies quite a bit with some dropping support as soon as the O/S goes into its End of Life status.
However, if you are aware and need to continue to use Windows 7 without nag messages, Microsoft has been kind enough to give you the option to not remind you again. This is a BIG improvement over the last transition when Windows 10 was released.
If you'd rather deal with this another way, you can also check for the KB patch that implements the, otherwise good, warning message. it will be KB4493132. You can also remove this patch on Win7 via the updates history.
You can also have a look at this article if you would like more info...