Add boilerplate checking to hook

hooks/boilerplate.sh

@@ -0,0 +1,13 @@
+#!/bin/bash
+
+# Print 1 if the file in $1 has the correct boilerplate header, 0 otherwise.
+FILE=$1
+LINES=$(cat "$(dirname $0)/boilerplate.txt" | wc -l)
+DIFFER=$(head -$LINES "${FILE}" | diff -q - "$(dirname $0)/boilerplate.txt")
+
+if [[ -z "${DIFFER}" ]]; then
+  echo "1"
+  exit 0
+fi
+
+echo "0"