Doc: Add full path to the Default encoding option

Explain why the field might still show "System"
even though "UTF-8" is now the default.

Change-Id: I2960d4cb86405d122ee31690a07e7a57176d093d
Reviewed-by: David Schulz <david.schulz@digia.com>

doc/src/editors/creator-editors-options-text.qdoc

@@ -79,11 +79,15 @@
 
     \section2 File Encoding
 
-    To define the default file encoding, select a suitable option in
+    To define the default file encoding, select \gui Tools > \gui Options >
+    \gui {Text Editor} > \gui Behavior, and then select a suitable option in
     \gui {Default encoding}.
 
     Qt 5 requires UTF-8 encoded source files, and therefore the default
     encoding was changed from \gui System to \gui UTF-8 in \QC version 2.6.
+    However, the \gui {Default encoding} field still displays the value
+    \gui System if the default system encoding is set to UTF-8.
+
     Detecting the correct encoding is tricky, so \QC will not try to do so.
     Instead, it displays the following error message when you try to edit a file
     that is not UTF-8 encoded: \gui {Error: Could not decode "filename" with