document the state of the calendars in one place

docs/calendars.md: the three independent questions a reckoning answers, how
the 1923 split came about and the three changes since that catch out a printed
reference, which churches keep what, and where the line falls between the
Byzantine rite and the nine Eastern Catholic churches that do not use it.

The README and --list lose the prose that had grown around the same subject.

README.md

@@ -174,28 +174,9 @@ See [the law and the fast](#the-law-and-the-fast-are-not-the-same-question)
 for what `--typikon` does with this, which is the flag most Byzantine Catholics
 will want.
 
-### The other ten
-
-There are fourteen Byzantine-rite Eastern Catholic churches. The Slovak,
-Hungarian, Krizevci, Italo-Albanian, Greek, Bulgarian, Macedonian, Belarusian,
-Russian and Albanian ones are **not** here, and the reason is worth stating:
-their calendars could not be verified against anything published. General
-references do not record them, and the churches' own sites render their
-liturgical calendars in JavaScript. Guessing from geography would put an
-unsourced claim in the one place this program is actually for.
-
-You do not need an entry to get a correct calendar. Ask your parish one
-question, and the answer picks a reckoning:
-
-| is Pascha kept with… | and the fixed feasts… | |
-|---|---|---|
-| Rome | on the civil calendar | `--calendar western` |
-| the local Orthodox | on the civil calendar | `--calendar new` |
-| the local Orthodox | thirteen days behind | `--calendar old` |
-
-Add `--tradition slavic` or `--tradition greek` for the usage your books
-follow. A patch adding your church, with a source for its calendar, is
-welcome.
+Ten of the fourteen Byzantine-rite Eastern Catholic churches have no entry of
+their own. Each keeps one of the three reckonings, and
+[docs/calendars.md](docs/calendars.md) sets out which questions decide it.
 
 ## The fast
 
@@ -442,6 +423,11 @@ $ typikon --update-menaion ruthenian
 
 It lands in `~/.local/share/typikon/` and is overlaid automatically.
 
+## Further reading
+
+[docs/calendars.md](docs/calendars.md) sets out which churches keep which
+reckoning, how the split came about, what is modelled here and what is not.
+
 ## Accuracy
 
 `typikon` is pinned against published calendars: the paschalion for six years