command: document enum command_mode

Add the description to doxygen documentation.

Change-Id: Iec04b4a37088e1b3b52ca84102820f450528b5b9
Signed-off-by: Antonio Borneo <borneo.antonio@gmail.com>
Reviewed-on: https://review.openocd.org/c/openocd/+/6593
Tested-by: jenkins

src/helper/command.h

@@ -38,6 +38,15 @@
 #define PRINTF_ATTRIBUTE_FORMAT printf
 #endif
 
+/**
+ * OpenOCD command mode is COMMAND_CONFIG at start, then switches to COMMAND_EXEC
+ * during the execution of command 'init'.
+ * The field 'mode' in struct command_registration specifies in which command mode
+ * the command can be executed:
+ * - during COMMAND_CONFIG only,
+ * - during COMMAND_EXEC only,
+ * - in both modes (COMMAND_ANY).
+ */
 enum command_mode {
 	COMMAND_EXEC,
 	COMMAND_CONFIG,