diff --git a/README.md b/README.md
index 8aabb43..dc0c78b 100644
--- a/README.md
+++ b/README.md
@@ -2,6 +2,11 @@
 
 This python script is intended to be used to automatically generate use case / correlation rule documentation in Markdown format for the McAfee Enterprise Sceurity Manager (ESM). It accepts a XML file that has been exported from the correlation rule editor of the ESM, converts its contents to Markdown format and writes it into a new file. If you need any other format, you might want to use pandoc to convert to e.g. pdf, docx or HTML.
 
+## Requirements
+
+This tool requires lxml (https://github.com/lxml/lxml).
+On Debian you can install it with "sudo apt-get install python3-lxml"
+
 ## Usage
 
 ```