Doc: Edited Qt Help page and clarified .qhp file location.
Doc: Edited Qt Help page and clarified .qhp file location.

-replaced "html" with "HTML"
-noted that the .qhp files are in the HTML directories

Task-number: QTBUG-29576
Change-Id: I0ba1c9534d730648c25dcdf15fcb1448fa9eb8fc
Reviewed-by: Leena Miettinen <885fda02d52616fec24ed5fed9b3f0568fce3ead@digia.com>

mer-qt/qttools,mer-qt/qttools,mer-qt/qttools,mer-qt/qttools,mer-qt/qttools,mer-qt/qttools