show the thing: screenshots, and a harness that makes them

Nobody installs a desktop widget they have not seen. Three shots go in the
README -- the Nativity Fast, where the week runs through three fasting
levels; ROCOR on 7 January, where the corner reads 25 December and makes the
old-calendar point in one glance; and Great Week, which uses nearly every
level there is.

shot.qml renders the real widget on a plain backdrop at a fixed position on
the overlay layer, so a screen grab of that rectangle is the widget and never
whatever was behind it. Typikon gains a forDate property, which is what lets
a screenshot show Great Week in September, and is worth having anyway for
looking ahead.

The header note now always carries the church date instead of repeating the
season the line below it already gives.

README.md

@@ -8,6 +8,8 @@ Everything is computed locally by `typikon`, so none of this touches the
 network, and the widget re-reads only when the date rolls over — the answer
 changes at midnight and at no other moment.
 
+![The widget during the Nativity Fast](docs/nativity-fast.png)
+
 ## Install
 
 `typikon` first, since all three front ends shell out to it:
@@ -107,17 +109,25 @@ set your own before the `@import`.
 ## What it shows
 
 The feast or the day's principal commemoration, the fast and why, the season,
-the week ahead, and Pascha. Two details worth pointing out:
+the week ahead, and Pascha.
 
-- **The church date** appears beside the civil one whenever they differ, which
-  on the old calendar is always. 25 December and 7 January are the same feast.
-- **Forefeasts, afterfeasts and leave-takings** get their own quiet line rather
-  than crowding out the commemoration that makes the day itself. They repeat
-  for days at a time.
+**The church date is always in the corner.** On the new calendar it echoes the
+wall calendar; on the old it is the answer you came for. Below, ROCOR on 7
+January — which is 25 December, and the Nativity.
 
-The legend is built from the week in view rather than hardcoded, because the
+![The Nativity on the old calendar](docs/old-calendar.png)
+
+**Forefeasts, afterfeasts and leave-takings** get their own quiet line rather
+than crowding out the commemoration that makes the day itself. They repeat for
+days at a time, and a widget that leads with "Post-festive Day of the
+Exaltation" for a week has told you nothing.
+
+**The legend is built from the week in view**, not hardcoded, because the
 levels a tradition uses are its own — six under the Typikon, three under
-Ruthenian particular law — and the words for them differ too.
+Ruthenian particular law — and the words for them differ too. Great Week uses
+nearly all of them:
+
+![Great and Holy Week](docs/great-week.png)
 
 ## Licence