Update gitignore to ignore md files for AI agents

OpenStack uses .rst for docs, so .md files can all
be ignored, which covers the AGENT.md files used for
AI coding assistants.

Change-Id: Iebf485894c391a0f38d5a8314a79c1e3a41d6b7c
Signed-off-by: Emma Foley <efoley@redhat.com>
diff --git a/.gitignore b/.gitignore
index 59b35f5..1290bc3 100644
--- a/.gitignore
+++ b/.gitignore
@@ -57,3 +57,7 @@
 
 # Files created by releasenotes build
 releasenotes/build
+
+# Files used by AI agents for instructions, rules and project context
+# md is also used for docs, but we can ignore them since openstack uses rst
+*.md