Updated build instructions.
diff --git a/README.md b/README.md
index 8174c4d..5455d02 100644
--- a/README.md
+++ b/README.md
@@ -6,7 +6,15 @@
     $ gem install middleman
     $ bundle install
 
-All sources are in the `/source` directory
+All sources are located in the `/source` directory. The build process requires JavaScript engine to be installed. For Ubuntu Linux use:
+
+```bash
+sudo apt-get update
+sudo apt install nodejs
+```
+
+For more details look at: 
+https://github.com/sstephenson/execjs/issues/71
 
 Build the site with: