improving doc

README.md

@@ -823,9 +823,21 @@ returning.
 *while watching a signal*: the time window, pause/resume, the trigger toggle, the
 side-panel toggle and an overflow menu. Those
 four buttons are icons with tooltips; nine text buttons was a wall of words to read
-past every time you wanted the one you needed. The overflow menu holds **Fit to
-data**, the **Layout editor**, **Cursors**, **Reset cursors**,
-**Export visible range…** and the **Signal list** toggle — the things you set up once. The side column and the two panel toggles stay hidden until a
+past every time you wanted the one you needed. The overflow menu holds **Fit to data**, the
+**Layout editor**, the **Signal list** toggle, **Export visible range...**, **Keyboard
+shortcuts**, **Help** and **About udpscope**, in that order — the shape a GNOME menu has, and
+drawn as one: every row's label starts at the same left edge (and the rows that can be checked
+keep that column whether or not they are checked), a shortcut sits at the row's right edge, a row
+is ~18 px tall rather than Adwaita's 34, and the groups are separated by rules. The ⓘ on the
+status bar opens its detail **above** the button: below is off the window's bottom edge, and a
+bubble whose body is clipped away while its top edge stays at the button is what "the arrow is
+detached from the body" looks like.
+
+The **help window** (`F1`) carries the same screenshots as `docs/`: the overview page shows the
+main window and a held capture above its text, and the trigger and math pages carry theirs. A
+page's images are `GtkPicture`s **with a height request** — a shrinkable one asks for no height at
+all inside a box, so without it the page renders its text with a silent gap where the screenshots
+should be. The side column and the two panel toggles stay hidden until a
 CONFIG arrives — there is nothing to configure before the stream describes itself —
 and the first CONFIG reveals the signal panel (the trigger panel stays behind its
 own toggle).