users: Clarify .stignore is only read from the folder root (#835)

This is a follow up to https://forum.syncthing.net/t/is-it-correct-that-stignore-inside-a-subfolder-is-not-applied/20997

Co-authored-by: André Colomb <[email protected]>

users/ignoring.rst

@@ -16,11 +16,13 @@ Description
 -----------
 
 If some files should not be synchronized to (or from) other devices, a file called
-``.stignore`` can be created containing file patterns to ignore. The
-``.stignore`` file must be placed in the root of the synced folder. The
-``.stignore`` file itself will never be synced to other devices, although it can
-``#include`` files that *are* synchronized between devices. All patterns are
-relative to the synced folder root.
+If some files should not be synchronized to (or from) other devices, a file called
+``.stignore`` can be created containing file patterns to ignore.  The ``.stignore``
+file must be placed in the root of the synced folder (files in other locations are
+not applied).  The ``.stignore`` file itself will never be synced to other devices,
+although it can ``#include`` files that *are* synchronized between devices.  All
+patterns are relative to the synced folder root.  The contents of the ``.stignore``
+file must be UTF-8 encoded.
 The contents of the ``.stignore`` file must be UTF-8 encoded.
 
 .. note::