Add a readme file

Add a basic readme file with information about the mod.

Also add the screenshot of the mod from the forum topic to the readme.

README.md

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+# Maidroid
+Maidroid is a mod for Minetest which adds maid robots that can perform common tasks such as farming and cutting down trees.
+
+![A screenshot of maid robots from the Maidroid mod](screenshot_readme.png)
+
+## Dependencies
+* default
+* dye
+
+## Forum Topic
+The forum topic for this mod on the Minetest Forums is located at:
+
+* https://forum.minetest.net/viewtopic.php?f=9&t=14808
+
+## License
+The source code of Maidroid is available under the [GPLv3](https://www.gnu.org/licenses/gpl-3.0.html) or later license.
+
+The resouces included in Maidroid are available under the [CC-BY-SA 4.0](https://creativecommons.org/licenses/by-sa/4.0/) or later license.