Document soundbank findings

docs/user-guide.md

@@ -26,6 +26,8 @@ back with one click.
   sound's name (useful hints for the many unlabelled lines); tick *Include characters mentioned in names*
   to filter on them too.
 - Click a column header to sort (length, size, status, ...). Ctrl/Shift-click selects several rows.
+- Most short effects (footsteps, foley, weapons, menu sounds) are stored inside soundbanks and are not listed
+  yet; the list covers voice lines, music, ambience and the effects of the SFX archive.
 - **Language** (top left) switches the speech language. Speech is read from the language the game is set to.
 
 ![Browsing by category](img/browse.png)