'git mv' rst resources to md

This is mainly intended to keep the git history as neat as possible.
No actual conversion yet, so now both the rst and the paradox docs
are broken, which will be fixed in the next commits.

akka-docs/src/main/paradox/intro/index-java.md

@@ -0,0 +1,13 @@
+Introduction
+============
+
+.. toctree::
+   :maxdepth: 2
+
+   what-is-akka
+   why-akka
+   getting-started
+   ../java/hello-world
+   deployment-scenarios
+   use-cases
+