Add an extra prerequisite - ruby2.x-dev in docs/README.md (#1820)

* Add an extra prerequisite - ruby2.x-dev

Trying to install Jekyll on my Linux (Ubuntu 16.04) machine failed because ```ruby 2.x``` was installed and ```ruby2.x-dev``` was not. I spent a lot of time trying to figure it out (I'm no ruby expert) but installing the ```ruby2.x-dev``` solved my problem.

* Add a note for Ubuntu users

diff --git a/docs/README.md b/docs/README.md
index ba661bb355ede0af2cff5d16368f66f27b41528a..ca1567ff617842fe1bbdea3dbb8211cf4a6ae58b 100644 (file)
--- a/docs/README.md
+++ b/docs/README.md
@@ -5,6 +5,8 @@ The documentation HTML is produced with the Ruby-based `jekyll` tool.
 1. Make sure Ruby 2.x is installed.
 2. `gem install jekyll`
 
+> **Note**: If you are an ```Ubuntu user``` Make sure ruby2.x-dev is installed
+
 ## Viewing the documentation locally
 
 Then to view the documentation in your local checkout: