Docs: size the display supply for the power-on inrush

A 12 V 1 A adapter browns out at start-up: the datasheet's inrush current
is 5x the 550 mA maximum, about 2.75 A at 12 V. List the supply current per
voltage and recommend 12 V 3 A, 12 V 2 A with a bulk capacitor, or 24 V.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

README.md

@@ -82,10 +82,26 @@ through a MAX3232. The [desk case](case/README.md) is made for that board.
 
 ### Power
 
-The display takes 5–24 V. At 5 V it draws about 0.8 A typical and 1.2 A
+The display takes 4.5–26 V. Its supply current with all dots lit (datasheet
-maximum, and the inrush current at power-on can be up to five times that. A
+section 4.6):
-dev-board regulator can't supply this, so give the display its own supply,
+
-for example 12 V at 1 A, and connect the grounds together.
+| Supply | Typical | Maximum | Inrush at power-on (5 × max) |
+|--------|---------|---------|------------------------------|
+| 5 V    | 0.8 A   | 1.2 A   | up to 6 A                    |
+| 12 V   | 0.35 A  | 0.55 A  | up to 2.75 A                 |
+| 24 V   | 0.2 A   | 0.3 A   | up to 1.5 A                  |
+
+The inrush current sets the size of the supply, not the running current. A
+12 V 1 A adapter is **not enough**: it current-limits at power-on and the
+display browns out during start-up. A dev-board regulator can't supply this
+either, so give the display its own supply and connect the grounds together:
+
+- **12 V, 3 A or more** (recommended). The D1 R1 can share it through its
+  barrel jack, which accepts up to 12 V.
+- **12 V, 2 A plus a bulk capacitor** of 2200 µF / 25 V or more across VCC and
+  GND at the display connector, so the capacitor supplies the inrush peak.
+- **24 V, 2 A.** This has the lowest current, but don't feed it to the D1 R1's
+  barrel jack: power the board separately, e.g. over USB.
 
 ### Signal levels