docs: fix html end/start tags

for more well-formed html

Signed-off-by: Brian Paul <brianp@vmware.com>

docs/helpwanted.html

@@ -55,14 +55,14 @@ Then post a message to propose what you want to do, just to make sure
 there's no issues.
 </p>
 
-</p>
+<p>
 Anyone is welcome to contribute code to the Mesa project.
 By doing so, it's assumed that you agree to the code's licensing terms.
 </p>
 
 <p>
 Finally:
-<p>
+</p>
 
 <ol>
 <li>Try to write high-quality code that follows the existing style.