diff --git a/database/README.md b/database/README.md
index 54e921e..ba4572d 100644
--- a/database/README.md
+++ b/database/README.md
@@ -1,5 +1,12 @@
 # Database files
 
-Please download the database files [here](https://cdn.bertold.org/zonedetect/db/db.zip) or create them using the builder. 
+Please download the database files [here](https://cdn.bertold.org/zonedetect/db/db.zip) or create them using the builder.
+
+To use the builder, first install [shapelib](https://github.com/OSGeo/shapelib), then:
+
+    cd database/builder
+    ./makedb.sh
+    
+This will create database files in `out` and `out_v1`, as well as a `db.zip` containing both directories.
 
 The files in the folder out\_v1/ use a newer format and use less space to encode the same information.