Adding sample file mentioned in README

prepare-vms/settings/example.yaml

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+# customize your cluster size, your cards template, and the versions
+
+# Number of VMs per cluster
+clustersize: 5
+
+# Jinja2 template to use to generate ready-to-cut cards
+cards_template: cards.html
+
+# Use "Letter" in the US, and "A4" everywhere else
+paper_size: Letter
+
+# Feel free to reduce this if your printer can handle it
+paper_margin: 0.2in
+
+# Note: paper_size and paper_margin only apply to PDF generated with pdfkit.
+# If you print (or generate a PDF) using ips.html, they will be ignored.
+# (The equivalent parameters must be set from the browser's print dialog.)
+
+# This can be "test" or "stable"
+engine_version: test
+
+# These correspond to the version numbers visible on their respective GitHub release pages
+compose_version: 1.18.0
+machine_version: 0.13.0