Add warning that I'm not an active maintainer

Author: seanmiddleditch

README.md

@@ -1,6 +1,13 @@
 setup-vsdevenv
 ==============
 
+> [!CAUTION]
+> I am generally an absentee maintainer. I update this package if and when I
+> personally need an update. It may be *years* before I see or respond to your
+> issues or pull  request. I do not recommend that you rely on this package for
+> critical infrastructure. If you find this action useful and do want to use it,
+> I suggest that you make a copy of it into your own repository.
+
 [GitHub Action](https://github.com/features/actions) for setting Visual Studio
 build environment variables and paths for subsequent steps in the job.