update manual

manual.md

@@ -22,14 +22,14 @@ In the code editor, a few special characters can be inserted by holding alt whil
 
 Symbols for arrows:
 
-- `⬆️`
-- `⬅️`
-- `⬇️`
-- `➡️`
+- `⬆️` (Alt+W)
+- `⬅️` (Alt+A)
+- `⬇️` (Alt+S)
+- `➡️` (Alt+D)
 
 And math symbols:
 
-- `π`
+- `π` (Alt+P)
 
 ### Graphics