Syntax highlighting of code blocks with markdown

When you write comments or Readme on github, you can add an optional language identifier to enable syntax highlighting.

For example, for Ruby code:

```ruby
def initialize(budget:, start_date: Time.zone.today, end_date:)
  @budget = budget
  @end_date = end_date
  @start_date = start_date
end
```

and the result will be:

Imgur