Added a resource about Accessibility

[lucalanca]

I was searching through some links and I couldn't find any link regarding accessibility. I think this is quite an important point of modern web applications so I added one link (Disclaimer: I'm the author of the article).

Formatting

Please follow the existing formatting for each entry. In order to get newlines without paragraph breaks, each entry should have two spaces at the end of the line after both the URL and the title. Also, two-space indents before the URL and the description. Example:

- **Link Title**<space><space>  
<space><space>http://example.com<space><space>  
<space><space>Link description here

Result:

• Link Title
  http://example.com
  Link description here

Please do not strip whitespace for existing entries!