README.md: Modify steps of Usage

This modifies the steps required to build and run
the website on the local machine by suggesting not
to use sudo in the command to install jekyll and
bundler and prefer asdf-vm to install ruby.

Closes coala#477

README.md

@@ -29,15 +29,26 @@ Why?
 
 ## Usage
 
-To clone the repository and run this website on your local machine, [install Jekyll](https://jekyllrb.com/docs/installation/) for your OS and type the following commands:
+### Dependencies
 
-    $ sudo gem install jekyll bundler
+1. Install [asdf-vm](https://asdf-vm.github.io/asdf/#/core-manage-asdf-vm) for your OS.
+2. Using asdf-vm, install [ruby](https://github.com/asdf-vm/asdf-ruby).
+3. Install Jekyll
+
+        $ gem install jekyll bundler
+
+### Clone and Run
+
+Clone coala Projects repository
+
     $ git clone https://github.com/coala/projects.git
+
+Run coala Projects website
+
     $ cd projects
     $ bundle install
     $ bundle exec jekyll serve
 
-
 Then you can simply go to either of the following addresses in your browser to access the site:
 
     127.0.0.1:4000