Enable adbd on microdroid

The following system properties are forcibly set to make adbd function.

ro.apex.updatable=true : otherwise, apexd doesn't activate critical
APEXes like the runtime APEX

ro.adb.secure=0 : to bypass the adb authentication

ro.debuggable=1 : to be able to use ro.adb.secure=0

This change also updates README.md file for the instruction to use adb.

Bug: 181728474
Test: adb shell works towards microdroid. See microdroid/README.md

Change-Id: Ica405e8bd4d2d1ef03e545aef5ed07ddc4bea34c
diff --git a/microdroid/Android.bp b/microdroid/Android.bp
index d0c6675..7bb1d4a 100644
--- a/microdroid/Android.bp
+++ b/microdroid/Android.bp
@@ -46,6 +46,7 @@
     deps: [
         "init_second_stage",
         "microdroid_init_rc",
+        "ueventd.rc",
         "libbinder",
         "libstdc++",
         "logcat",