This patch further improves the `gui/manual/intro.txt` file:
* "building" → "structure"
* "Hide/show" and "Show/hide" → "Toggle"
* "panel" (something that is fixed) → "window" (something that can open and close)
* added a few missing entries
* reordered some items because of position on keyboard
* several minor corrections
It is a follow-up to D2110/rP22904 and earlier.
https://trac.wildfiregames.com/wiki/HotKeys is already updated in advance.