Add one more CONTRIBUTING item

CONTRIBUTING.md

@@ -8,6 +8,7 @@ When making a pull request, please follow these guidelines:
 - Lists within each section are alphabetized
 - Add sections if necessary
 - Clear, concise descriptions for each link, followed by a period
+- Use the following format: `[Item Name](homepage link) - Description.`
 - No duplication of tools, put them where they make the most sense
 - Wrap lines at ~80 chars, no trailing whitespace or unnecessary newlines
 - Prefer quality over quantity, only submit awesome stuff