Link fifty gestures on the help sheet to the manual section that shows them

The sheet could now offer "See it", but no gesture said where to look.

Every GESTURE tag whose move the manual describes names that section:
the white-balance picker, zoom and pan, masks, undo and snapshots,
export, colour labels and ratings, selection, collections, the People
page, thumbnail size. Fifty of the fifty-one; the one left, putting a
single control back to its default, has no section and is too small to
earn one.

Three important gestures had nowhere to land, so the manual gains three
short sections, without pictures for now: Bursts (opening a folded
burst, choosing the frame it shows, and the eyes-open filter), Moving
between photographs (the roll, the arrows and A/D in develop) and
Copying settings (Copy, Paste, Paste to N, and choosing what a copy
carries). The page, the gesture book and docs/gestures.md are
regenerated from them.

docs/manual/README.md

@@ -94,6 +94,16 @@ move back to the top level, keep it offline, delete.
 
 ![The menu on a collection](media/library-collection-menu.png)
 
+### Bursts
+
+Frames taken a moment apart that look alike fold into one cell, with a badge
+counting them. Click the badge — tap it, on a tablet — to open the burst in
+the grid, and again to fold it back. A folded burst shows its earliest frame;
+to have it show another, open it and click the ring on the frame you want.
+
+With faces indexed, narrowing the grid to a person puts `Eyes open` beside
+their name on the filter bar, which leaves out the frames where they blinked.
+
 ## Developing a photograph
 
 Click a thumbnail to open it. The column on the right is every adjustment;
@@ -117,6 +127,13 @@ wheel zooms to any amount in between.
 
 ![Zooming to 1:1, panning, and back](media/develop-zoom.gif)
 
+### Moving between photographs
+
+The roll along the foot of the canvas holds the photographs the grid was
+showing; click one to open it. The right arrow, `D` or space opens the next,
+and the left arrow or `A` the one before. The edit on screen is saved on the
+way, so stepping along a shoot loses nothing.
+
 ### White balance from the photograph
 
 Press `pick` in the White Balance group, then click something neutral —
@@ -178,6 +195,15 @@ apply elsewhere, and imports `.xmp` from other applications.
 
 ![The presets sheet](media/presets.png)
 
+### Copying settings
+
+`Copy` in the top bar, or Ctrl+C, takes this photograph's settings; `Paste`,
+or Ctrl+V, puts them on another, and says what it would paste — how many
+adjustments, and whether the crop comes too. In the grid, `Paste to N` on the
+selection bar pastes onto every photograph selected. Which kinds of edit a
+copy carries is chosen in `Presets…`, or with Ctrl+Shift+C: a look carried
+across a shoot usually leaves each frame's own crop alone.
+
 ## Merging a panorama
 
 Select the frames, then `Merge to panorama` from the selection bar. The