Add Ender-5 leadscrew README (#16424)

config/examples/Creality/Ender-5/README.md

+# Creality Ender-5 Leadscrew Changes
+
+In mid-to-late 2019, Creality upgraded the base Ender-5 leadscrew to the same one used on the Ender-5 Pro which prevents the bed from dropping once power is cut.
+
+If your machine shipped with the upgraded leadscrew (or if your prints are 1/2 as tall as they should be), change your Z steps from `400` to `800` in `Configuration.h`:
+
+Before:
+`DEFAULT_AXIS_STEPS_PER_UNIT   { 80, 80, 400, 93 }`
+
+After:
+`DEFAULT_AXIS_STEPS_PER_UNIT   { 80, 80, 800, 93 }`
+
+Or by sending `M92 Z800` followed by `M500` after updating your firmware.