Bug 19747: Add link to article requests help page

Bug 19747: Add link to article requests help page

Newer manuals contain information about article requests.
This patch adds the link to the article request section
in the manual.

To test:
- Activate ArticleRequests system preference
- Go to Circulation > Article requests
- Click on Help
- Verify that you end up in the proper section of the manual

Signed-off-by: Michal Denar <black23@gmail.com>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>