Updated readme

README.txt

@@ -6,6 +6,9 @@ syntax: lem3edit <level_number>
 place the binary in the same directory as L3CD.EXE
 on case-sensitive filesystems, all the data files must have upper case filenames
 
+Use the left mouse button to select and place objects from the object bar.
+Click on objects in the level to select them, and then drag selected objects to move them.
+
 == Keys ========================================================================
 s             -- save level
 q             -- quit
@@ -16,11 +19,14 @@ escape        -- select none
 delete        -- delete selected objects
 ctrl + c      -- copy
 ctrl + v      -- paste
+
+1             -- switch object bar to background and object pieces
+2             -- switch object bar to terrain pieces
 z             -- scroll object bar left
 x             -- scroll object bar right
 
 scroll-wheel  -- zoom in and out
 b             -- toggle background-only mode
 ijkl          -- scroll
-arrow pad     -- move objects
+arrow pad     -- fine-tune object location
 shift         -- ... faster