[Documentation] Add instruction how to execute built-in commands of various shells.

(cherry picked from commit 9faf1e027a26cb1207d635a45ab153502722ae54)

doc/classes/OS.xml

@@ -115,6 +115,9 @@
 				OS.execute("CMD.exe", ["/C", "cd %TEMP% && dir"], true, output)
 				[/codeblock]
 				[b]Note:[/b] This method is implemented on Android, iOS, Linux, macOS and Windows.
+				[b]Note:[/b] To execute a Windows command interpreter built-in command, specify [code]cmd.exe[/code] in [code]path[/code], [code]/c[/code] as the first argument, and the desired command as the second argument.
+				[b]Note:[/b] To execute a PowerShell built-in command, specify [code]powershell.exe[/code] in [code]path[/code], [code]-Command[/code] as the first argument, and the desired command as the second argument.
+				[b]Note:[/b] To execute a Unix shell built-in command, specify shell executable name in [code]path[/code], [code]-c[/code] as the first argument, and the desired command as the second argument.
 			</description>
 		</method>
 		<method name="find_scancode_from_string" qualifiers="const">