runtime(doc): all secure options should note this restriction in the documentation (#13448)

Problem:  Not all secure options document their status
Solution: Describe secure context :set restrictions in each help entry

Signed-off-by: Doug Kearns <dougkearns@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>

runtime/doc/options.txt

@@ -1604,6 +1604,8 @@ A jump table for the options with a short description can be found at |Q_op|.
 	current working directory to the |$HOME| directory like in Unix.
 	When off, those commands just print the current directory name.
 	On Unix this option has no effect.
+	This option cannot be set from a |modeline| or in the |sandbox|, for
+	security reasons.
 	NOTE: This option is reset when 'compatible' is set.
 
 						*'cdpath'* *'cd'* *E344* *E346*
@@ -5590,7 +5592,8 @@ A jump table for the options with a short description can be found at |Q_op|.
 <	If you have less than 512 Mbyte |:mkspell| may fail for some
 	languages, no matter what you set 'mkspellmem' to.
 
-	This option cannot be set from a |modeline| or in the |sandbox|.
+	This option cannot be set from a |modeline| or in the |sandbox|, for
+	security reasons.
 
 				   *'modeline'* *'ml'* *'nomodeline'* *'noml'*
 'modeline' 'ml'		boolean	(Vim default: on (off for root),
@@ -5992,6 +5995,8 @@ A jump table for the options with a short description can be found at |Q_op|.
 				*'packpath'* *'pp'*
 'packpath' 'pp'		string	(default: see 'runtimepath')
 	Directories used to find packages.  See |packages|.
+	This option cannot be set from a |modeline| or in the |sandbox|, for
+	security reasons.
 
 
 						*'paragraphs'* *'para'*
@@ -6076,6 +6081,8 @@ A jump table for the options with a short description can be found at |Q_op|.
 			feature}
 	Expression which is evaluated to apply a patch to a file and generate
 	the resulting new version of the file.  See |diff-patchexpr|.
+	This option cannot be set from a |modeline| or in the |sandbox|, for
+	security reasons.
 
 					*'patchmode'* *'pm'* *E205* *E206*
 'patchmode' 'pm'	string	(default "")
@@ -7158,6 +7165,8 @@ A jump table for the options with a short description can be found at |Q_op|.
 	When 'shellxquote' is set to "(" then the characters listed in this
 	option will be escaped with a '^' character.  This makes it possible
 	to execute most external commands with cmd.exe.
+	This option cannot be set from a |modeline| or in the |sandbox|, for
+	security reasons.
 
 						*'shellxquote'* *'sxq'*
 'shellxquote' 'sxq'	string	(default: "";
@@ -8214,6 +8223,8 @@ A jump table for the options with a short description can be found at |Q_op|.
 	function and an example.  The value can be the name of a function, a
 	|lambda| or a |Funcref|. See |option-value-function| for more
 	information.
+	This option cannot be set from a |modeline| or in the |sandbox|, for
+	security reasons.
 
 						*'taglength'* *'tl'*
 'taglength' 'tl'	number	(default 0)
@@ -8973,6 +8984,8 @@ A jump table for the options with a short description can be found at |Q_op|.
 	Setting 'verbosefile' to a new value is like making it empty first.
 	The difference with |:redir| is that verbose messages are not
 	displayed when 'verbosefile' is set.
+	This option cannot be set from a |modeline| or in the |sandbox|, for
+	security reasons.
 
 						*'viewdir'* *'vdir'*
 'viewdir' 'vdir'	string	(default for Amiga: "home:vimfiles/view",