Using: add a pointer about the cover letter

Author: phil-blain

index.html

@@ -100,7 +100,7 @@ <h2>How can you use GitGitGadget?</h2>
 				So you cloned <a href="https://github.com/git/git">https://github.com/git/git</a> and implemented a bug fix or a new feature?
 				And you already pushed it to your own fork?
 				Good, now is the time to direct your web browser to <a href="https://github.com/gitgitgadget/git">https://github.com/gitgitgadget/git</a> (or to <a href="https://github.com/gitgitgadget/git">https://github.com/git/git</a> ) and to open a Pull Request.
-				Please make sure to use a descriptive Pull Request title and description; GitGitGadget will use these as the cover letter.
+				Please make sure to use a descriptive Pull Request title and description; GitGitGadget will use these as the subject and body of the cover letter (check out the <a href="https://git-scm.com/docs/MyFirstContribution">MyFirstContribution</a> tutorial if you are not familiar with this terminology).
 				You can CC potential reviewers by adding a footer to the PR description with the following syntax:
 				<pre>CC: Revi Ewer &lt;revi.ewer@some.domain&gt;, Ill Takalook &lt;ill.takalook@other.domain&gt;</pre>
 			</p><p>