Update README explaining that the layout needs a gyroscope (#9)

* Update README explaining that the layout needs a gyroscope

Author: rocboronat

README.md

@@ -155,6 +155,9 @@ For bugs, requests, questions and discussions please use [Github Issues](https:/
 # Attributions
 This library was developed by [Rafa Vázquez](https://github.com/Sloy/) with the idea of moving images from [Alex Bailón](https://github.com/abailon) for the [Infojobs' Android application](https://play.google.com/store/apps/details?id=net.infojobs.mobile.android).
 
+# Device requirements
+This layout needs a gyroscope powered device. Sadly, there are some low-end phones that doesn't have it. In that case, the layered will appear like a static image.
+
 # License
 
 ```