README: jam behavior + where the jam lamp lives (field-confirmed)

Live verification closed the loop on issue #30: heat-jammed SRMs light
the authentic BTEJAM lamp on the weapon panel's ENG DATA page; the
default view shows nothing (authentic).  Testers get told where to look.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

players/README.txt

@@ -42,6 +42,10 @@ CONTROLS (keyboard):
   3 or Ctrl ............ upper thumb (missiles) 4 ............ pinky
   V view | B look-behind | M control mode | N schematic | J/K/L MFD pages
   - / = ................ game volume down/up (saved between sessions)
+  A weapon gone quiet with ammo left has probably JAMMED (heat makes
+  ballistic weapons jam -- authentic!).  Check its panel's ENG DATA page
+  for the jam lamp (a cocked round with warning bolts).  Jams last the
+  mission; a respawn clears them.  Watch the TEMP strip and pace salvos.
   G (hold) + fire key .. regroup a weapon onto that trigger -- or hold a
      weapon panel's red PROGRAM button with the mouse and tap a fire key;
      the joystick diagram on the panel shows the binding live.