userguide: add a note to both “exec”s about semicolon and comma

fixes #1678

docs/userguide

@@ -724,6 +724,10 @@ commands will not run when restarting i3, if you need a command to run
 also when restarting i3 you should use the +exec_always+
 keyword. These commands will be run in order.
 
+See <<command_chaining>> for details on the special meaning of +;+ (semicolon)
+and +,+ (comma): they chain commands together in i3 and need to be escaped if
+you want to use them in your command.
+
 *Syntax*:
 -------------------
 exec [--no-startup-id] command
@@ -1467,6 +1471,8 @@ do this is to use the +i3-msg+ utility:
 i3-msg border none
 --------------------------
 
+[[command_chaining]]
+
 Commands can be chained by using +;+ (a semicolon). So, to move a window to a
 specific workspace and immediately switch to that workspace, you can configure
 the following keybinding:
@@ -1540,7 +1546,11 @@ information on how to use them.
 What good is a window manager if you can’t actually start any applications?
 The exec command starts an application by passing the command you specify to a
 shell. This implies that you can use globbing (wildcards) and programs will be
-searched in your $PATH.
+searched in your +$PATH+.
+
+See <<command_chaining>> for details on the special meaning of +;+ (semicolon)
+and +,+ (comma): they chain commands together in i3 and need to be escaped if
+you want to use them in your command.
 
 *Syntax*:
 ------------------------------