Add note about dependencies and generation

README.md

@@ -4,8 +4,16 @@
 
 This is just the script to generate a combined PDF from the currently-online-chapters available for review.
 
+The script also takes care of putting in the right bookmarks for all the chapters in the generated PDF file.
+
 Go read the book from the source at <https://www.cl.cam.ac.uk/~rja14/book.html>
 
+## How to generate the book?
+
+Run `./generate.sh`. You will need `pdftk`, and `wget` installed.
+
+Once the script finishes running, check the `security-engineering-3rd-edition.pdf` file.
+
 ## Support the Authors
 
 Buy the second editions from:

generate.sh

@@ -1,5 +1,16 @@
 #!/bin/bash
 
+function assert_installed() {
+    for var in "$@"; do
+        if ! which $var &> /dev/null; then
+            echo "Install $var!"
+            exit 1
+        fi
+    done
+}
+
+assert_installed wget pdftk
+
 COVER_URL=https://www.cl.cam.ac.uk/~rja14/Papers/SEv3-cover.jpg
 
 # wget --timestamping  "$COVER_URL" --output-document cover.jpg