samples/cgroup: add .gitignore file for generated samples

Make 'git status' quietly happy again after a full allmodconfig build.

Fixes: 60433a9d038d ("samples: introduce new samples subdir for cgroup")
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/samples/cgroup/.gitignore b/samples/cgroup/.gitignore
new file mode 100644
index 0000000..3a01611
--- /dev/null
+++ b/samples/cgroup/.gitignore
@@ -0,0 +1,3 @@
+/cgroup_event_listener
+/memcg_event_listener
+