Add Ruby on Rails v6 example which uses Webpacker

[amree]

Add an example for Ruby on Rails v6 which uses webpacker to handle its javascript. The current example is the older version which uses an asset pipeline, so, a different example is needed for the newer version of Ruby on Rails.

p/s: I can create two commits to make it clearer, one to create the project and the other is for adding TradingView's integration. I don't think we should update the current Ruby on Rails example. I think lots of people are still using that version.

Add example checklist

• [x] Any commit does not contain the charting library's code
• [ ] Addresses an existing issue: #00000
• [x] The example is added to README.md
• [x] The example is self-sufficient and contains only necessary files/changes

Bug fix checklist

• [ ] Any commit does not contain the charting library's code
• [ ] Addresses an existing issue: #00000