add git-churn script

bin/git-churn

@@ -0,0 +1,23 @@
+#!/bin/bash
+#
+# Written by Corey Haines
+# Scriptified by Gary Bernhardt
+#
+# Put this anywhere on your $PATH (~/bin is recommended). Then git will see it
+# and you'll be able to do `git churn`.
+#
+# Show churn for whole repo:
+#   $ git churn
+#
+# Show churn for specific directories:
+#   $ git churn app lib
+#
+# Show churn for a time range:
+#   $ git churn --since='1 month ago'
+#
+# (These are all standard arguments to `git log`.)
+
+set -e
+git log --all -M -C --name-only --format='format:' "$@" | sort | grep -v '^$' | uniq -c | sort | awk 'BEGIN {print "count\tfile"} {print $1 "\t" $2}' | sort -g
+
+