Clarify drag-n-drop behaviour again (#3434)

* Clarify drag-n-drop behaviour again

Just found the real reason of drag-n-drop issue mentioned in
b89e8d1635.

* Trying to formulate correctly

editions/tw5.com/tiddlers/features/Drag and Drop.tid

@@ -17,6 +17,8 @@ Tiddler manipulation via drag and drop is supported by the core user interface i
 
 All tiddler links are draggable by default. They can be dragged within a browser window for manipulating tiddlers, or dragged to a different browser window to initiate an [[import operation|Importing Tiddlers]]
 
+If you want to drag a link, first move it vertically, because horizontal movement is recognized by the browser as text selection.
+
 Tag pills are also draggable, and are equivalent to simultaneously dragging all of the individual tiddlers carrying the tag.
 
 Some common scenarios for drag and drop tiddler manipulation are available as reusable macros:

editions/tw5.com/tiddlers/learning/Copying tiddlers between TiddlyWiki files.tid

@@ -6,4 +6,4 @@ type: text/vnd.tiddlywiki
 
 You can copy an individual tiddler from one TiddlyWiki file to another by dragging a link to the tiddler from one browser window to another.
 
-Depending on your browser, dragging may not work and moving the mouse only highlights the text. In this case you should hold down the left mouse key on the link, wait a second, and then try again to drag it.
+If you want to drag a link, first move it vertically, because horizontal movement is recognized by the browser as text selection.