Add README at top of repository with links to others.

Test: looked at README in Markdown preview.
Change-Id: I254f9ea81d6dbc0267f2d2d3b36f779a55dc03cd
diff --git a/README.md b/README.md
new file mode 100644
index 0000000..eb28e94
--- /dev/null
+++ b/README.md
@@ -0,0 +1,6 @@
+# Virtualization
+
+This repository contains userspace services related to running virtual machines on Android,
+especially protected virtual machines. See the
+[getting started documentation](docs/getting_started/index.md) and
+[Microdroid README](microdroid/README.md) for more information.