Update README

Author: Christian Griset

README.md

@@ -25,6 +25,9 @@ repos:
 # - it either
 #   (a) makes changes to files within the repo, outputs a commit message to stdout, and exits with code 0
 #   (b) exits with a nonzero exit code
+
+# Basepath to prepend temp directories. Not including this option is okay and the program will assume ""
+base_path: "path/to/prepend/tmpdir"
 change_cmds:
   # command paths can either be absolute paths, or paths relative to the configuration file.
   - path: "/path/to/the/program"