Basic documentation for android.system.

Also individually @hide the methods we might not want to expose straight
away. These are basically the ones where the mapping to Java types isn't
completely straightforward, usually resulting in a family of similar methods.

Change-Id: I7b3d555c4599dc8c64e23f5c494a358ef68c6777
diff --git a/Docs.mk b/Docs.mk
index c1e793b..612b3d9 100644
--- a/Docs.mk
+++ b/Docs.mk
@@ -19,6 +19,7 @@
    json/src/main/java \
    libdvm/src/main/java/dalvik \
    libdvm/src/main/java/java \
+   luni/src/main/java/android \
    luni/src/main/java/java \
    luni/src/main/java/javax \
    luni/src/main/java/org/xml/sax \