docs: add note for URI Segments

Author: kenjis

user_guide_src/source/libraries/uri.rst

@@ -204,7 +204,13 @@ to an on-page anchor. Media URI's can make use of them in various other ways.
 URI Segments
 ============
 
-Each section of the path between the slashes is a single segment. The URI class provides a simple way to determine
+Each section of the path between the slashes is a single segment.
+
+.. note:: URI Segments mean only the URI path part relative to the baseURL. If
+    your baseURL contains sub folders, the values will be different from the
+    current URI path.
+
+The URI class provides a simple way to determine
 what the values of the segments are. The segments start at 1 being the furthest left of the path.
 
 .. literalinclude:: uri/023.php