Activity does not work, but add README.md anyway

Basic README.md for pointing contributors to the migrated wiki.
Complete documentation may in future be available at https://help.sugarlabs.org/en/ruler.html

README.md

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+# Activities/Ruler - Sugar Labs
+
+##About Ruler
+Ruler is a simple collection of measurement tools that are displayed on the screen. 
+
+## How to get?
+
+ Ruler is an activity of the Sugar desktop. For more information refer to:
+
+* [How to Get Sugar](https://sugarlabs.org/)
+* [How to use Sugar](https://help.sugarlabs.org/)
+* [How to use Ruler](https://help.sugarlabs.org/en/ruler.html)
+
+## How to upgrade?
+
+On Sugar desktop systems;
+
+* Use [My Settings](https://help.sugarlabs.org/en/my_settings.html), [Software Update](https://help.sugarlabs.org/en/my_settings.html#software-update), or;
+* Use Browse to open [activities.sugarlabs.org](https://activities.sugarlabs.org/), search for `Ruler` and click `Download Now`.
+
+## Request a new feature
+
+* Head over to [sugarlabs/ruler/issues](https://github.com/sugarlabs/ruler/issues) and open up a new issue, giving detailed information about what you have in mind. 
+
+## GPL license 
+
+This code is under [General Public Licence v3](https://github.com/sugarlabs/ruler/blob/master/COPYING)