Add dexgen project dir

Adds a home directory and description for the dexgen project which aims to
provide API for runtime dex classes generation which is necessary e.g for class
mocking. It is mostly based on dx tool classes.

Change-Id: I92b02e38f305b94ad088ec8a8a8899b1d600268d
diff --git a/dexgen/README.txt b/dexgen/README.txt
new file mode 100644
index 0000000..a542f04
--- /dev/null
+++ b/dexgen/README.txt
@@ -0,0 +1,3 @@
+Home of dexgen, the dex code generator project. It provides API for
+creating dex classes in runtime which is needed e.g. for class mocking.
+This solution is based on the dx tool and uses its classes extensively.