Order entry

Clicks on the board, because that is where the question is. Select a unit,
pick a verb, and the provinces the next click will accept light up. Nobody
writes a move the rules were never going to allow, and nobody has to learn a
notation to find that out.

What is offered comes from the rules rather than from the map, which is the
same split the map is built on: a fleet on the north coast of Spain is drawn
identically to one on the south coast and can go to entirely different
places. A support is only offered where both units could have gone, since you
cannot support a move you could not have made yourself, and a fleet is only
asked which coast it means when more than one is reachable.

Orders are drawn where they are given -- an arrow to the destination, a
dashed line to what a support is holding up, a ring round a unit staying put
-- and written out beside the board in the rules' own words, because an arrow
cannot tell you that the support you meant for Vienna is going to Budapest.
The written list runs through the validator on every keystroke, so an order
the rules will not take is struck through while it is being written rather
than after the turn.

README.md

@@ -178,6 +178,25 @@ refused to make that offer would be playing a politer game than this one. It
 will not, however, ask the power it is attacking to *help*, or offer it peace
 while the orders say otherwise.
 
+## Giving orders
+
+Clicks on the board, because that is where the question is. Select a unit,
+pick a verb, and the provinces the next click will accept light up -- so
+nobody writes a move the rules were never going to allow, and nobody has to
+learn a notation to find that out.
+
+Everything offered comes from the rules rather than from the map, which is
+the same split the map itself is built on. A fleet on the north coast of
+Spain is drawn identically to one on the south coast and can go to entirely
+different places; no shape can express that, and the highlight has to.
+
+Orders are drawn where they are given: an arrow to where a unit is going, a
+dashed line to what a support is holding up, a ring round a unit that is
+staying. The list beside the board says the same thing in the rules' own
+words, because an arrow cannot tell you that the support you meant for Vienna
+is being given to Budapest. Anything the rules will not take is struck
+through in the list as it is written, rather than after the turn.
+
 ## Still to build
 
 - the map, the orders, the music, the battle sound, the four endings