updated ebook details

ruby_one_liners.md

@@ -50,13 +50,17 @@
     * [Executing external commands](#executing-external-commands)
 * [Further Reading](#further-reading)
 
+<br> <br> <br>
+
 ---
 
 :information_source: :information_source: This chapter has been converted into a better formatted ebook - https://learnbyexample.github.io/learn_ruby_oneliners/. The ebook also has content updated for newer version of `ruby`, extra chapter for parsing json/csv/xml, includes exercises, solutions, etc.
 
+For markdown source and links to buy pdf/epub versions, see: https://github.com/learnbyexample/learn_ruby_oneliners
+
 ---
 
-<br>
+<br> <br> <br>
 
 ```
 $ ruby --version