env: Move the doc comment to the code

This doesn't really make much sense in the documentation. Add a code
comment instead.

Suggested-by: Heinrich Schuchardt <xypron.glpk@gmx.de>

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/common/autoboot.c b/common/autoboot.c
index b8861d5..63f2587 100644
--- a/common/autoboot.c
+++ b/common/autoboot.c
@@ -446,6 +446,11 @@
 	s = env_get("bootdelay");
 	bootdelay = s ? (int)simple_strtol(s, NULL, 10) : CONFIG_BOOTDELAY;
 
+	/*
+	 * Does it really make sense that the devicetree overrides the user
+	 * setting? It is possibly helpful for security since the device tree
+	 * may be signed whereas the environment is often loaded from storage.
+	 */
 	if (IS_ENABLED(CONFIG_OF_CONTROL))
 		bootdelay = ofnode_conf_read_int("bootdelay", bootdelay);
 
diff --git a/doc/usage/environment.rst b/doc/usage/environment.rst
index d295cc8..4b228c1 100644
--- a/doc/usage/environment.rst
+++ b/doc/usage/environment.rst
@@ -120,7 +120,6 @@
     The default value is defined by CONFIG_BOOTDELAY.
     The value of 'bootdelay' is overridden by the /config/bootdelay value in
     the device-tree if CONFIG_OF_CONTROL=y.
-    Does it really make sense that the devicetree overrides the user setting?
 
 bootcmd
     The command that is run if the user does not enter the shell during the