include: Added some basic documentation so SDL_KeyCode shows up on the wiki.

Fixes #11525.

include/SDL_keycode.h

@@ -41,12 +41,18 @@
  *
  * A special exception is the number keys at the top of the keyboard which map
  * to SDLK_0...SDLK_9 on AZERTY layouts.
+ *
+ * The actual values that might be set for this type are listed in the
+ * SDL_KeyCode (capital C) enumeration.
  */
 typedef Sint32 SDL_Keycode;
 
 #define SDLK_SCANCODE_MASK (1<<30)
 #define SDL_SCANCODE_TO_KEYCODE(X)  (X | SDLK_SCANCODE_MASK)
 
+/**
+ * The possible values for keycodes.
+ */
 typedef enum SDL_KeyCode
 {
     SDLK_UNKNOWN = 0,