Add an initial README.md, so that the repository is no longer empty.

Author: kbeyls

README.md

@@ -0,0 +1,7 @@
+This is a test repository to experiment with GitHub's "privately reporting a
+security vulnerability" workflow, see
+<https://docs.github.com/en/code-security/security-advisories/guidance-on-reporting-and-writing-information-about-vulnerabilities/privately-reporting-a-security-vulnerability>
+
+If or when security vulnerabilities or advisories appear against this specific
+repository, they are expected to be as a result of experimenting with this
+workflow and not be actual vulnerabilities.