tool: Add error for write locked

Add a new error for the case of trying to flash when security is enabled
and it is still locked and update the related docs.

Signed-off-by: Tim Crawford <tcrawford@system76.com>

src/board/system76/common/security.c

@@ -11,7 +11,7 @@ enum SecurityState security_get(void) {
 
 bool security_set(enum SecurityState state) {
     switch (state) {
-    // Allow perpare states to be set
+    // Allow prepare states to be set
     case SECURITY_STATE_PREPARE_LOCK:
     case SECURITY_STATE_PREPARE_UNLOCK:
         security_state = state;