Doc: provide an example of how 3rdparty/hunspell should look

It can be difficult to get the directory structure right, so having
this example will make it easy for the user to check if they’ve
copied in the Hunspell sources correctly.

Change-Id: I15dbafff37f44c2ea24d24077d8387898dd49ca3
Reviewed-by: Jarkko Koivikko <jarkko.koivikko@code-q.fi>
Reviewed-by: Mitch Curtis <mitch.curtis@qt.io>

src/virtualkeyboard/doc/src/build.qdoc

@@ -264,6 +264,23 @@ then the dictionary files must also be copied into the
 \e src/virtualkeyboard/3rdparty/hunspell/data directory. Furthermore, if Hunspell
 sources are used, \e hunspell.pro will be used for all targets.
 
+An example of how the directory structure should look after copying in the
+Hunspell sources and dictionary files is listed below:
+
+\badcode
+3rdparty
+└── hunspell
+    ├── data
+    │   ├── en_GB.aff
+    │   └── en_GB.dic
+    ├── hunspell.pro
+    └── src
+        └── hunspell
+            ├── affentry.cxx
+            ├── affentry.hxx
+            (etc.)
+\endcode
+
 \section2 Static builds
 
 The virtual keyboard can be built and linked statically against the application.