Fix examples "make install", missing the doc files.

Change-Id: Ifcfc888782e2087476f6f65388db5cda753e0ee7
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@digia.com>

examples/assistant/simpletextviewer/simpletextviewer.pro

@@ -11,4 +11,7 @@ SOURCES       = main.cpp \
 QT += widgets
 
 target.path = $$[QT_INSTALL_EXAMPLES]/assistant/simpletextviewer
-INSTALLS += target
+docs.files += $$PWD/documentation
+docs.path = $$target.path
+
+INSTALLS += target docs

examples/help/contextsensitivehelp/contextsensitivehelp.pro

@@ -11,4 +11,7 @@ HEADERS += wateringconfigdialog.h \
 FORMS   += wateringconfigdialog.ui
 
 target.path = $$[QT_INSTALL_EXAMPLES]/help/contextsensitivehelp
-INSTALLS += target
+docs.files += $$PWD/doc
+docs.path = $$target.path
+
+INSTALLS += target docs