stop lending Ruthenian law to churches it was never written for

Three Eastern Catholic jurisdictions borrowed the Ruthenian ruleset, so a
Melkite, a Romanian Greek Catholic and a Ukrainian Greek Catholic were each
told that fourteen days a year bound them under the particular law of the
Metropolia of Pittsburgh. That is the exact error the level/obligation split
exists to prevent, committed by the library itself.

Every Eastern Catholic church legislates its own fasting discipline. Those
three are now shown at the Typikon with nothing reported as binding, which is
the honest position: the calendar is known, the law is not. Their entries say
so and a test holds it, asserting both that no jurisdiction but ruthenian
carries that ruleset and that the three claim no binding days.

The README gains a section on these churches, since supporting them was never
meant to be something a reader had to infer from the jurisdiction list.

README.md

@@ -1,7 +1,8 @@
 # typikon
 
 The Orthodox liturgical day: feasts, seasons and the fast, computed rather
-than fetched.
+than fetched. The Byzantine Catholic churches are here too, on their own
+calendars and, where the law has been sourced, under their own particular law.
 
 Everything derives from the paschalion and the fixed calendar, so it needs no
 network, cannot go stale, and answers for any year you ask about. No API key,
@@ -149,6 +150,30 @@ Bulgaria, Cyprus, Albania, Ukraine), the Finnish Orthodox Church, alone among
 the Orthodox in keeping the Gregorian Paschalion, and, as an add-on, four
 Byzantine Catholic churches.
 
+## The Byzantine Catholic churches
+
+Four are modelled, and they are not a footnote on the Orthodox ones: they keep
+different paschalions, and their fasting is a different kind of thing.
+
+| | calendar | fasting |
+|---|---|---|
+| `ruthenian` | Gregorian throughout | Ruthenian particular law, sourced |
+| `ugcc` | Revised Julian feasts, Julian Pascha since 2023 | its own; not modelled |
+| `melkite` | Gregorian; Middle Eastern parishes often keep Julian Pascha | its own; not modelled |
+| `romanian-catholic` | Gregorian throughout | its own; not modelled |
+
+**A church's law is never borrowed from another.** Ruthenian particular law is
+sourced from the Metropolia of Pittsburgh and is reported for that church only.
+The rest are shown at the Typikon's discipline with **nothing reported as
+binding**, because their own law has not been sourced and inventing one would
+tell a Melkite that fourteen days a year oblige him under a law that was never
+his. When a church's law is added, its entry will say so and its obligations
+will appear. A test holds that line.
+
+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 fast
 
 Six levels, ordered from strictest to laxest. They are the Typikon's own