Unclear description of QHG_LOCATION

The description of `QHG_LOCATION` is a bit unclear (compare with `HHC_LOCATION`).
(based on https://stackoverflow.com/questions/64795335/qhelpgenerator-with-doxygen-keep-showing-sh-1-permission-denied/64801829#64801829)

src/config.xml

@@ -2297,7 +2297,9 @@ The \c DOCSET_PUBLISHER_NAME tag identifies the documentation publisher.
     <option type='string' id='QHG_LOCATION' format='file' defval='' depends='GENERATE_QHP'>
       <docs>
 <![CDATA[
- The \c QHG_LOCATION tag can be used to specify the location of Qt's qhelpgenerator.
+ The \c QHG_LOCATION tag can
+ be used to specify the location (absolute path including file name) of
+ Qt's qhelpgenerator.
  If non-empty doxygen will try to run qhelpgenerator on the generated `.qhp` file.
 ]]>
       </docs>