Describe flagging, scrollbars, Help and long steps in the manual

The manual described what the pictures show and missed what this round
changed around them:

- Rating and flagging gave stars only. The keys (0-5, P, X, U), Flag on
  the selection bar, judging in develop without moving on, and the flag
  and stars on the roll's cells had no sentence.
- Nothing said the desktop draws scrollbars on the grid, the sidebar,
  the develop column and Settings, or how the grid's bar is used.
- Nothing said how to open Help: the header's Help or F1, and in
  develop the "?" beside Settings (d9f2596, 380cfda), with its See it
  links and its Manual button.
- Stepping along the roll now goes on past what the roll has loaded
  (a030bfd); Settings gained the duplicate originals line and the
  Manual row.

index.html is regenerated from the README.

docs/manual/README.md

@@ -39,7 +39,13 @@ file is (on this device, or only on the server).
 ### Rating and flagging
 
 Hover a cell and the stars appear; click one. The filter chips above the grid
-count what each rating holds, and clicking `3+` shows only those.
+count what each rating holds, and clicking `3+` shows only those. From the
+keyboard, `0` to `5` set the stars on the photograph under the pointer or on
+the selection; `P` picks, `X` rejects and `U` takes the flag off, and `Flag`
+on the selection bar does the same with the pointer. In
+develop the same keys judge the open photograph and stay on it, and the top
+bar carries its stars and `Pick` and `Reject`; the roll marks each frame's
+flag and stars.
 
 ![Rating two photographs, then filtering the grid to three stars and more](media/library-rating.gif)
 
@@ -56,7 +62,14 @@ and the same keys work there.
 ### Getting about
 
 Drag the timeline to scrub through years; Ctrl and the wheel resize the
-thumbnails.
+thumbnails. On a desktop a scrollbar beside the grid says how far through the
+library the view is — drag its thumb, or click the track to move a page — and
+the sidebar, the develop column and Settings have one too whenever they run
+past the window. On a tablet they scroll by flick alone.
+
+`Help` in the header, or `F1`, opens the controls and shortcuts: every key and
+gesture, screen by screen, with `See it` beside those this page shows, and
+`Manual` to open this page. In develop it is the `?` beside `Settings`.
 
 ![Scrubbing the timeline](media/library-timeline.gif)
 
@@ -166,8 +179,9 @@ the sensor recorded.
 
 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.
+and the left arrow or `A` the one before; held down, they go on past the
+stretch the roll has loaded, through everything the grid would show. The
+edit on screen is saved on the way, so stepping along a shoot loses nothing.
 
 ### White balance from the photograph
 
@@ -286,9 +300,10 @@ set is refused, and the header says so.
 
 ![The settings page: background activity, indexing, storage, display](media/settings.png)
 
-Background activity with progress, thumbnail and face indexing, storage on
-this device, display and colour, export defaults, what is written to XMP
-sidecars, and a diagnostics bundle for a bug report.
+Background activity with progress, thumbnail and face indexing, how many
+duplicate originals the library holds and the way to their review, storage
+on this device, display and colour, export defaults, what is written to XMP
+sidecars, the manual, and a diagnostics bundle for a bug report.
 
 ## People