diff --git a/README.md b/README.md
index 6a7cbc2..d7a8619 100644
--- a/README.md
+++ b/README.md
@@ -15,3 +15,14 @@ Usage
   $ stt -s      # stop task
   $ stt [-l]    # print report
 
+Files
+-----
+
+If current working directory contains a `.ttimes` file it will be used
+otherwise it will create or use `~/.ttimes`.
+
+File format looks like:
+
+	<start-unix-timestamp>;<end-unix-timestamp>;<task>
+
+Zero value end timestamp means task is still running.