[guide] Add guide to menu

visidata/features/menu_guide.py

@@ -0,0 +1,29 @@
+from visidata import GuideSheet, vd
+
+class MenuGuide(GuideSheet):
+    guide_text = '''# The Menu System
+
+Located at the [:black on 68]very top of the screen[/], it contains a collection of commands organised within submenu trees.
+
+The menu can be navigated both as a standard, clickable GUI menu, and via keystrokes.
+
+To navigate via keystrokes, `Alt+H` will open the **Help** menu, and from there `↑ ↓ → ←` keys can be used to move between submenus.
+
+Additionally, each top-level menu name has a single letter underlined. `Alt+<underlined letter>` will open that menu. For example, `Alt+F` will open the **File** menu.
+
+`{vd.options.disp_menu_more}` indicates a submenu, which can be traversed with the `→` or a mouse-click. The leaf node of every menu tree is a command.
+
+When the cursor is on a command, the menu throws up its [:color_menu_help]helpbox[/]. This contains the description of the command, the keyboard shortcut if available, and its command longname. Clicking on the command in the menu, or pressing `Enter`, will execute the actual command.
+
+`{vd.options.disp_menu_push}` indicates that the command will push a sheet onto sheet stack. `{vd.options.disp_menu_input}` indicates that input will be required for the command.
+
+[:color_menu_spec]Sheet-specific commands[/] will only appear in the menu when that specific sheet type is loaded.
+
+## Options
+
+- {help.options.disp_menu}
+- {help.options.disp_menu_fmt}
+- {help.options.color_menu}
+'''
+
+vd.addGuide('MenuGuide', MenuGuide)