Add some basic docs

book/src/remapping.md

@@ -19,6 +19,13 @@ w = "move_line_up" # Maps the 'w' key move_line_up
 g = { a = "code_action" } # Maps `ga` to show possible code actions
 "ret" = ["open_below", "normal_mode"] # Maps the enter key to open_below then re-enter normal mode
 
+# You can create labeled sub-menus and provide friendly labels for typeable commands
+[keys.normal.space.f] # Registering multiple mappings under a single entry creates a sub-menu (accesed by 'space', 'f' in this case)
+label = "File" # The menu is called file and within  it:
+f = "file_picker" # 'f' opens the file picker
+s = { label = "Save", command = ":write" } # 's' saves the current file
+c = { label = "Edit Config", command = ":open ~/.config/helix/config.toml" } # 'c' opens the helix config file
+
 [keys.insert]
 "A-x" = "normal_mode"     # Maps Alt-X to enter normal mode
 j = { k = "normal_mode" } # Maps `jk` to exit insert mode