Document the KEY LOCK startup default setting

Author: dtavan

source/hardware/controllers/denon_mc3000.md

@@ -81,6 +81,8 @@ controller and the Denon MC3000 mapping:
   (default: `1.0`). Higher values reduce sensitivity.
 - **VINYL MODE on by default** sets whether {hwlabel}`VINYL MODE` is
   enabled by default at startup, for all four decks (default: off).
+- **KEY LOCK on by default** sets whether {hwlabel}`KEY LOCK` is
+  enabled by default at startup, for all four decks (default: off).
 
 ## Mixer Section
 
@@ -92,7 +94,7 @@ controller and the Denon MC3000 mapping:
 | {hwlabel}`FILTER` | QuickEffect filter. |
 | {hwlabel}`HI` / {hwlabel}`MID` / {hwlabel}`LOW` | 3-band channel EQ. |
 | {hwlabel}`CUE DECK A` / {hwlabel}`CUE DECK B` / {hwlabel}`CUE DECK C` / {hwlabel}`CUE DECK D` | Headphone cue (PFL) toggle, one button per deck letter. |
-| {hwlabel}`KEY LOCK` | Toggles keylock for the deck. |
+| {hwlabel}`KEY LOCK` | Toggles keylock for the deck. Off by default at startup for all four decks; see Mapping Settings above to change the default. |
 | {hwlabel}`SYNC` | Beat-syncs the deck. Hold past a short delay to enable continuous sync lock instead of a one-time sync. The LED lights while sync is active. |
 | {hwlabel}`SHIFT` + {hwlabel}`SYNC` | Toggles quantize for the deck. |