Docs: the row-height cap is conditional now, and the board's narrow-screen behaviour was nowhere in the page help

Plugin/unraid/pages/readme/monitor-readme.md

@@ -10,6 +10,22 @@ a minute, so polling faster could not make it newer — it only decides how soon
 **Cards you do not have do not appear.** No GPU, no UPS, no VMs, no partner — the card is absent
 rather than showing zeros. An empty card would be a permanent reminder of nothing.
 
+**The board re-flows on a narrow screen.** On a tablet or a phone the cards regroup into fewer,
+wider columns rather than shrinking in place. Nothing is hidden and nothing is dropped — the same
+cards are there in the same order, cut into different rows.
+
+Below the full-width layout the page scrolls as a whole instead of each card scrolling inside
+itself. A board that is taller than the screen has to scroll somewhere, and scrolling the page
+once is better than being handed a screen of cards that are each too short to read.
+
+**Cards in the same row share a height.** They line up along the bottom, so a card with little to
+say carries empty space under it. That space means its neighbour is the taller card — not that a
+reading is missing.
+
+The System card is the one exception. On a narrow screen it stops after Version and the Varaverk
+figures below scroll, so that the host itself — hostname, clock, array state, uptime — is what
+you get without scrolling anything.
+
 ---
 
 ## Reference — System, power, CPU, memory, network