Add footer to wiki documentation

Added footer to the wiki documentation.

Author: lvlindv

docs/wiki/_Footer.md

@@ -0,0 +1,5 @@
+**This wiki is being actively developed**
+
+If you discover any documentation bugs or would like to request new content, please raise them as an [issue](https://github.com/Azure/AzRegionSelection/issues).
+
+Contributions to this wiki are done through the main repo under [docs/wiki](https://github.com/Azure/AzRegionSelection).