add desc as an official Overlay API property

docs/dev/overlay-dev-guide.rst

@@ -89,11 +89,14 @@ The ``overlay.OverlayWidget`` superclass defines the following class attributes:
 - ``name``
     This will be filled in with the display name of your widget, in case you
     have multiple widgets with the same implementation but different
-    configurations.
+    configurations. You should not set this property yourself.
 - ``version``
     You can set this to any string. If the version string of a loaded widget
     does not match the saved settings for that widget, then the configuration
     for the widget (position, enabled status) will be reset to defaults.
+- ``desc``
+    A short (<100 character) description of what the overlay does. This text
+    will be displayed in `gui/control-panel` on the "Overlays" tab.
 - ``default_pos`` (default: ``{x=-2, y=-2}``)
     Override this attribute with your desired default widget position. See
     the `overlay` docs for information on what positive and negative numbers

plugins/lua/overlay.lua

@@ -553,6 +553,7 @@ end
 OverlayWidget = defclass(OverlayWidget, widgets.Panel)
 OverlayWidget.ATTRS{
     name=DEFAULT_NIL, -- this is set by the framework to the widget name
+    desc=DEFAULT_NIL, -- add a short description (<100 chars); displays in control panel
     default_pos={x=DEFAULT_X_POS, y=DEFAULT_Y_POS}, -- 1-based widget screen pos
     default_enabled=false, -- initial enabled state if not in config
     overlay_only=false, -- true if there is no widget to reposition
@@ -581,6 +582,7 @@ end
 
 TitleVersionOverlay = defclass(TitleVersionOverlay, OverlayWidget)
 TitleVersionOverlay.ATTRS{
+    desc='Show DFHack version number and quick links on the DF title page.',
     default_pos={x=11, y=1},
     version=2,
     default_enabled=true,