Add note on the need to restart after editing shell command (#40764)

Author: wojciechbielecki

source/_integrations/shell_command.markdown

@@ -36,12 +36,16 @@ alias:
   type: string
 {% endconfiguration %}
 
-The commands can be dynamic, using templates to insert values for arguments. When using templates, shell_command runs in a more secure environment which doesn't allow any shell helpers like automatically expanding the home dir `~` or using pipe symbols to run multiple commands. Similarly, only content after the first space can be generated by a template. This means the command name itself cannot be generated by a template, but it must be literally provided.
+The commands can be dynamic, using templates to insert values for arguments. When using templates, shell_command runs in a more secure environment which doesn't allow any shell helpers like automatically expanding the home directory character (`~`), using pipe symbols (`|`) to run multiple commands, or operators redirecting output (such as `>` and `>>`). Similarly, only content after the first space can be generated by a template. This means the command name itself cannot be generated by a template, but it must be literally provided.
 
 Any action data passed into the action to activate the shell command will be available as a variable within the template.
 
 `stdout` and `stderr` output from the command are both captured and will be logged by setting the [log level](/integrations/logger/) to debug.
 
+{% note %}
+After you add or edit a command, restart Home Assistant. New commands won’t work until you restart, and changes to existing commands won’t take effect until after a restart.
+{% endnote %}
+
 ## Execution
 
 The `command` is executed within the [configuration directory](/docs/configuration/).