[guide] Add guide to menu (#2168)

Author: anjakefala

visidata/guides/MenuGuide.md

@@ -0,0 +1,26 @@
+# The Menu System
+
+The menu (on the first row of the window) contains most commands, organized within a tree of submenus.
+
+Click on menu items to navigate the menu like a GUI.
+
+With the keyboard:
+
+- {help.commands.menu_help}
+- [:keys]Arrow[/] keys to move between submenus
+
+Additionally, each top-level menu name has a single letter underlined. [:keys]Alt+<underlined letter>[/] to open that menu. For example, [:keys]Alt+F[/] to open the **File** menu.
+
+Each non-submenu item is a command. It shows the description of the current command, along with the command name and its keyboard shortcut (if available). Click on the item or [:keys]Enter[/] to execute it.
+
+Indicators:
+
+- {help.options.disp_menu_more}
+- {help.options.disp_menu_push}
+- {help.options.disp_menu_input}
+
+Some commands are only available on a specific sheet type, and appear [:color_menu_spec]highlighted[/] in the menu when the current sheet is that type. If the command is not available, it will not appear at all.
+
+## Options
+
+- {help.options.disp_menu}

visidata/menu.py

@@ -499,7 +499,7 @@ def _clickedDuringMenu():
 BaseSheet.addCommand('Alt+d', 'menu-data', 'pressMenu("Data")', '')
 BaseSheet.addCommand('Alt+p', 'menu-plot', 'pressMenu("Plot")', '')
 BaseSheet.addCommand('Alt+s', 'menu-system', 'pressMenu("System")', '')
-BaseSheet.addCommand('Alt+h', 'menu-help', 'pressMenu("Help")', '')
+BaseSheet.addCommand('Alt+h', 'menu-help', 'pressMenu("Help")', 'open the Help menu')
 BaseSheet.bindkey('Ctrl+H', 'menu-help')
 BaseSheet.bindkey('KEY_BACKSPACE', 'menu-help')