The CODEOWNERS File is not useful

Github is complaining about "This file has errors" and is just noisy
and for that reason does not ping maintainers if a new issue/PR is
created.
Let's just rename it to MAINTAINERS file instead and update the
documentation.

Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/Filelist b/Filelist
index ff474bc..7718548 100644
--- a/Filelist
+++ b/Filelist
@@ -5,7 +5,7 @@
 SRC_ALL =	\
 		.cirrus.yml \
 		.gitattributes \
-		.github/CODEOWNERS \
+		.github/MAINTAINERS \
 		.github/ISSUE_TEMPLATE/bug_report.yml \
 		.github/ISSUE_TEMPLATE/feature_request.md \
 		.github/workflows/ci.yml \