diff --git a/requirements.txt b/requirements.txt
index b9602f13..53c65152 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -1,3 +1,6 @@
+# This file contains python only requirements to be installed with pip
+# Python pacakges that cannot be installed with pip (e.g. PyQT4) are not included.
+# Usage: pip install -r requirements.txt
 numpy>=1.8
 matplotlib>=1.3.1
 shapely>=1.3