fix: adding notes about leftovers (#65)

Signed-off-by: matttrach <matt.trachier@suse.com>

notes/leftover_check.md

@@ -0,0 +1,7 @@
+# Leftovers
+
+I ran into an error where we had reached the EIP limit because I forgot to clean up after a catastrophic failure testing locally.
+
+I decided that the best way to prevent this would be to fail the release if leftovers found anything.
+
+Leftovers is a tool for finding resources in AWS given a filter, it works really well and solves a lot of problems for infrastructure testing.