patch 8.2.1594: pull requests on github do not notify a maintainer

Problem:    Pull requests on github do not notify a maintainer.
Solution:   Add a CODEOWNERS file with a few initial entries.
diff --git a/Filelist b/Filelist
index cd1325f..bcf8f3d 100644
--- a/Filelist
+++ b/Filelist
@@ -10,6 +10,7 @@
 		.travis.yml \
 		.cirrus.yml \
 		.github/workflows/ci-windows.yaml \
+		.github/CODEOWNERS \
 		appveyor.yml \
 		ci/appveyor.bat \
 		ci/if_ver*.vim \